After completing this chapter, the reader should be able to
Discuss how the anatomy and physiology of the liver and pancreas affect interpretation of pertinent laboratory test results
Classify liver test abnormalities into cholestatic and hepatocellular patterns and understand the approach to evaluating patients with these abnormalities
Explain how hepatic and other diseases, as well as drugs and analytical interferences, cause abnormal laboratory test results for bilirubin
Understand hepatic encephalopathy and the role of serum ammonia in its diagnosis
Discuss the laboratory test abnormalities typically associated with hemochromatosis
Design and interpret a panel of laboratory studies to determine if a patient has active, latent, or previous viral hepatitis infection
Understand the significance and use of amylase and lipase in evaluating abdominal pain and pancreatic disorders
Discuss the role of Helicobacter pylori in peptic ulcer disease and the tests used to diagnose it
Discuss the tests and procedures used to diagnose Clostridioides difficile colitis
Hepatic and other gastrointestinal (GI) abnormalities can cause a variety of clinically significant diseases, in part because of their central role in the body’s biochemistry. This chapter provides an introduction to common laboratory studies used to investigate these diseases. Studies of the liver are roughly divided into those associated with (1) synthetic liver function, (2) excretory liver function and cholestasis, (3) hepatocellular injury, and (4) detoxifying liver function and serum ammonia. Specific tests may also be used to investigate specific disease processes, including viral hepatitis, primary biliary cholangitis (PBC), and hemochromatosis. This chapter also covers several tests for specific nonhepatic disease processes, including pancreatitis, Helicobacter pylori infection, and Clostridioides difficile colitis.
ANATOMY AND PHYSIOLOGY OF THE LIVER AND PANCREAS
The liver, located in the right upper quadrant of the abdomen, is the largest solid organ in the human body. It has two sources of blood.
The hepatic artery, originating from the aorta, supplies arterial blood rich in oxygen.
Portal veins carry the venous blood from the intestines to the liver. They transport absorbed toxins, drugs, and nutrients directly to the liver for metabolism.
The liver is divided into thousands of lobules (Figure 15-1). Each lobule is comprised of plates of hepatocytes (liver cells) that radiate from the central vein much like spokes in a wheel. Between adjacent liver cells formed by matching grooves in the cell membranes are small bile canaliculi. The hepatocytes continually form and secrete bile into these canaliculi, which empty into terminal bile ducts. Subsequently, like tiny streams forming a river, these bile ducts empty into larger and larger ducts until they ultimately merge into the common bile duct. Bile then drains into the gallbladder for temporary storage or directly into the duodenum.
The liver is a complex organ with a prominent role in all aspects of the body’s biochemistry. It takes up amino acids absorbed by the intestines, processes them, and synthesizes them into circulating proteins, including albumin and clotting factors. The liver is also involved in breaking down excess amino acids and processing byproducts, including ammonia and urea. The liver plays a similar role in absorbing carbohydrates from the gut, storing them in the form of glycogen, and releasing them as needed to prevent hypoglycemia. Most lipid and lipoprotein metabolism, including cholesterol synthesis, occurs in the liver. The liver is the primary location for detoxification and excretion of a wide variety of endogenous substances produced by the body (including sex hormones) as well as exogenous substances absorbed by the intestines (including a panoply of drugs and toxins). Thus, in patients with liver failure, standard dosing of some medications can lead to dangerously high serum concentrations and toxicity. The role of the liver in bilirubin metabolism is explored further later in the chapter.
With its double blood supply, large size, and critical role in regulating body metabolic pathways, the liver is affected by many systemic diseases. Although numerous illnesses affect the liver, it has tremendous reserve capacity and can often maintain its function despite significant disease. Furthermore, the liver is one of the few human organs capable of regeneration.
The pancreas is an elongated gland located in the retroperitoneum. Its head lies in close proximity to the duodenum, and the pancreatic ducts empty into the duodenum. The pancreas has both exocrine glands (which secrete digestive enzymes into the duodenum) and endocrine glands (which secrete hormones directly into the circulation).
The pancreatic exocrine glands produce enzymes that aid in digestion of proteins, fats, and carbohydrates (including trypsin, chymotrypsin, lipase, and amylase). Insufficient enzyme production (ie, pancreatic exocrine insufficiency) is associated with malabsorption of nutrients, leading to progressive weight loss and severe diarrhea. The glands also produce many hormones, including insulin and glucagon. Insufficient insulin production leads to diabetes mellitus. Thus, the pancreas plays an important role in digestion and absorption of food as well as metabolism of sugar. Like the liver, the pancreas has a tremendous reserve capacity; >90% glandular destruction is required before diabetes or pancreatic insufficiency develops.
INTRODUCTION TO LIVER TESTS AND THE LIVER FUNCTION TEST PANEL
Investigation of liver disease often begins with obtaining a panel of liver tests, generally referred to as the LFT panel or liver function tests (LFTs).1 This panel may vary slightly between hospitals and laboratories but generally includes the aminotransferases (previously referred to as transaminases), including aspartate aminotransferase (AST), alanine aminotransferase (ALT), bilirubin, alkaline phosphatase (ALP), and albumin. LFT is a misnomer because not all tests actually measure liver function (specifically, aminotransferases reflect liver injury).
Additionally, the liver has multiple functions, and different tests reflect these different functions. Table 15-1 divides liver tests into rough categories. Although there is considerable overlap between these categories, these divisions may provide an initial framework for understanding the LFT panel.
Categories of Liver Tests
MOST CLOSELY RELATED TESTS
PT/INR (clotting factors)
Excretion into the bile ducts and drainage into the duodenum (impairment of this process is defined as cholestasis)
This grouping of tests mirrors a division of liver diseases into two broad categories: cholestatic and hepatocellular. In cholestatic disease, there is an abnormality in the excretory function of the liver (ie, namely secretion of bile by hepatocytes and passage of bile through the liver and bile ducts into the duodenum). In hepatocellular disease, there is primary inflammation and damage to the hepatocytes themselves (eg, due to viral infection of the hepatocytes). These two categories may overlap because disease of the hepatocytes (hepatocellular processes), if severe enough, will also lead to derangement of bile secretion. However, the distinction between primarily cholestatic and primarily hepatocellular diseases and, in turn, LFT patterns, remains useful and fundamental. Further confusing is the fact that liver test results may be abnormal in patients with diseases that do not affect the liver.
The range of normal laboratory values used here is taken from Harrison’s Principles of Internal Medicine, 19th edition.2 Reference ranges may vary slightly between different laboratories, and most laboratories list their reference ranges along with laboratory results. Listed normal ranges are for adult patients; normal ranges for pediatric patients often have different values.
TESTS OF SYNTHETIC LIVER FUNCTION
As discussed previously, one of the functions of the liver is to synthesize proteins that circulate in the blood, including albumin and clotting proteins. Measurement of the levels of these proteins in the blood provides a reflection of the ability of the liver to synthesize them. The liver has an enormous reserve function so that it may synthesize normal amounts of proteins despite significant liver damage. Therefore, tests of synthetic function are not sensitive to low levels of liver damage or dysfunction. Inadequate protein synthetic function is mainly limited to hepatic cirrhosis, which is scarring of the liver that can result from years of alcohol abuse, inflammation, or massive liver damage (eg, due to alcoholic liver disease, severe acute viral hepatitis, autoimmune hepatitis, unrecognized and untreated chronic hepatitis, or potentially lethal toxin ingestion). In these situations, measuring synthetic function may be useful in determining prognosis by reflecting the degree of hepatic failure. The most commonly used tests of protein synthetic function are albumin, prothrombin time (PT), and International Normalized Ratio (INR). An example of this is the Model for End-stage Liver Disease score, which uses the prothrombin time/INR (PT/INR) to help assess the severity of a patient’s liver disease and has been used to prioritize patients awaiting liver transplants.
Normal range: 4 to 5 g/dL (40 to 50 g/L)
Albumin is a major plasma protein that is involved in maintaining plasma oncotic pressure and the binding and transport of numerous hormones, anions, drugs, and fatty acids. The normal serum half-life of albumin is about 20 days, with about 4% degraded daily.3 Because of albumin’s long half-life, serum albumin measurements are slow to fall after the onset of hepatic dysfunction (eg, complete cessation of albumin production results in only a 25% decrease in serum concentrations after 8 days). For this reason, levels are often normal in acute viral hepatitis or drug-related hepatotoxicity. Alternatively, albumin is commonly reduced in patients with chronic synthetic dysfunction caused by cirrhosis.
Albumin levels may be low due to a variety of other abnormalities in protein synthesis, distribution, and excretion, in addition to liver dysfunction. These abnormalities include malnutrition/malabsorption; protein loss from the gut, kidney, or skin (as in nephrotic syndrome, protein-losing enteropathy, or severe burns, respectively); or increased blood volume (eg, following administration of large volumes of intravenous [IV] fluids). Albumin is a negative acute phase reactant, meaning that in the setting of systemic inflammation (eg, due to infection or malignancy), the liver produces less albumin, and there is a shifting of albumin out of the intravascular compartment. Severely ill, hospitalized patients commonly have low albumin levels due to a combination of poor nutrition, systemic inflammation, and IV fluid administration. In these patients, extremely low albumin concentrations carry a poor prognosis regardless of any particular liver disease. Although hypoalbuminemia is common in these patients, there is little evidence to support replacement simply for a low albumin concentration. Given the numerous causes of a low albumin level, it is important to interpret it within the context of each patient. For example, in a patient with metastatic cancer and no known liver disease, a low albumin level suggests decreased nutritional intake and advanced malignancy with systemic inflammation. Alternatively, in a patient with known cirrhosis, a low albumin level suggests severe chronic liver failure. While a low albumin level is commonly found in elderly patients with suboptimal nutrition, it may also suggest the presence of significant disease and requires further consideration and often investigation.
Hypoalbuminemia itself is usually not associated with specific symptoms or findings until concentrations become quite low. At very low concentrations (<2 to 2.5 g/dL), patients can develop peripheral edema, ascites, or pulmonary edema. Albumin normally generates oncotic pressure, which holds fluid in the vasculature. Under conditions of low albumin, fluid leaks from the vasculature into the interstitial spaces of subcutaneous tissues or into the body cavities. Calcium is bound to albumin, so a decrease in serum albumin may be associated with a decrease in total calcium concentrations, but the ionized (ie, free) calcium concentration usually does not change. In the presence of hypoalbuminemia, measuring an ionized calcium level helps sort this out. Finally, in the presence of low albumin concentration, the percentage of nonprotein bound medication in the bloodstream is increased for highly protein-bound agents (eg, phenytoin, warfarin, and salicylates). This could result in increased pharmacologic effects or adverse effects from usual doses of these medications.
Hyperalbuminemia is seen in patients with marked dehydration (which concentrates their plasma), in which it is associated with concurrent elevations in blood urea nitrogen (BUN) and hematocrit. Patients taking anabolic steroids may demonstrate truly increased albumin concentrations, but those on heparin or ampicillin may have falsely elevated results with some assays. Perhaps the most common cause of hyperalbuminemia is iatrogenic, overzealous use of parenteral albumin, which may be associated with fluid overload. Otherwise, hyperalbuminemia is not associated with any symptoms.
Normal range: 17 to 34 mg/dL (170 to 340 mg/L)
Prealbumin is similar to albumin in several respects: it is synthesized primarily by the liver, involved in the binding and transport of various solutes (thyroxin and retinol), and affected by similar factors that affect albumin levels. The primary difference between the two proteins is that prealbumin has a short half-life (2 days, compared with 20 days for albumin) and a smaller body pool than albumin, making the former more rapidly responsive than albumin.4 Additionally, due to its high percentage of tryptophan and essential amino acids, prealbumin is more sensitive to protein nutrition than albumin and is less affected by liver disease or hydration status than albumin.5 In practice, prealbumin is generally used to assess protein calorie nutrition, which is discussed in more detail in Chapter 12.6
International Normalized Ratio and Prothrombin Time
Normal range: INR 0.9 to 1.1; PT 12.7 to 15.4 seconds
For an introduction to INR and PT, please see Chapter 17. These two tests measure the speed of a set of reactions in the extrinsic pathway of the coagulation cascade. Decreased synthesis or impaired activation of clotting factors correlates with prolonged reaction times and increased values of INR and PT. Both PT and INR are two different measures of the same set of reactions, with the INR being a derived index that takes into account variations between test reagents used in different laboratories. As such, INR is more precise and easily interpretable and replaces the use of the PT.
The liver is required for the synthesis of clotting factors (with the exception of factor VIII), many of which require a vitamin K cofactor for their activation. Therefore, either hepatic impairment or vitamin K deficiency may lead to a deficiency in activated clotting factors with subsequent prolongation of PT/INR. Both synthetic failure and vitamin K deficiency may also cause prolongation of activated partial thromboplastin time, which measures a different set of coagulation reactions in the intrinsic coagulation cascade, but to a much lesser degree than PT/INR.
The prolongation of PT/INR alone is not specific for liver disease. It can be seen in many situations, most of which interfere with the use of vitamin K, a cofactor required for the proper posttranslational activation of clotting factors II, VII, IX, and X. Because vitamin K is a fat-soluble vitamin, inadequate vitamin K in the diet or fat malabsorption as caused by cholestasis may cause hypovitaminosis. Many broad-spectrum antibiotics, including tetracyclines, may reduce vitamin K–producing flora in the gut. The anticoagulant agent warfarin interferes directly with vitamin K–dependent activation of clotting factors.
If the etiology of elevated PT/INR remains unclear despite obtaining additional coagulation tests, then the clinical approach is to provide parenteral vitamin K.7 Although commonly given as a subcutaneous injection, vitamin K (10 mg) can be given by slow IV infusion in patients with prolonged PT/INR with serious bleeding. If the PT/INR is prolonged due to malabsorption, warfarin, perturbed gut flora, or the absence of vitamin K in the diet, the PT/INR usually corrects by at least 30% within 24 hours. Alternatively, failure of PT/INR to normalize despite parenteral vitamin K suggests impaired synthetic liver function (Figure 15-2). Other factors that may cause a prolonged PT/INR that does not respond to parenteral vitamin K include inherited clotting factor deficiencies.
Because clotting factors are produced in excess of need and because the liver has tremendous synthetic reserves, only substantial hepatic impairment (>80% loss of synthetic capability) leads to decreased synthesis of these factors and subsequent clotting abnormalities. Thus, PT/INR, albumin, and prealbumin levels lack sensitivity and may remain normal in the face of substantial liver damage. However, they have considerable prognostic value if liver damage is sufficient to affect them. Unlike albumin (which responds slowly to hepatic insult), PT/INR responds within 24 hours to changes in hepatic status because of the short half-life of certain clotting proteins (ie, factor VII has a half-life of <6 hours). Thus, the PT/INR may become elevated days before other manifestations of liver failure and, likewise, may normalize before other evidence of clinical improvement. One use for determining PT/INR in liver disease is to provide prognostic data, generally in situations in which the cause of the elevated PT/INR is known; for example, with an acute acetaminophen overdose leading to hepatic failure.
In addition to serving as an LFT, PT/INR has direct clinical relevance in accessing a patient’s tendency to bleed spontaneously or as a result of surgical or diagnostic procedures. Bleeding is a dramatic complication of hepatic failure. When the PT/INR is significantly elevated, bleeding may be controlled or at least diminished by coagulation factors or fresh frozen plasma, which contains the needed activated clotting factors and often corrects the PT/INR temporarily.
CHOLESTATIC LIVER DISEASE
Cholestasis is a deficiency of the excretory function of the liver. As described previously, bile is normally secreted by hepatocytes into bile canaliculi, where it flows into larger bile ducts and eventually empties into the duodenum. Excretion of bile from the liver serves multiple purposes. Certain large lipophilic toxins, drugs, and endogenous substances are eliminated by secretion into the bile with eventual elimination in the feces. Bile salts also play an important role in dissolving and absorbing dietary fat-soluble vitamins and nutrients within the small intestine.
Failure of the excretory functions of the liver leads to a predictable set of consequences. Substances normally secreted in the bile accumulate, resulting in jaundice (from bilirubin), pruritus (from bile salts), or xanthomas (from lipid deposits in skin). Absence of bile salts to dissolve fat-soluble nutrients can lead to deficiencies of fat-soluble vitamins A, D, E, and K, which may result in osteoporosis (lack of vitamin D) and PT/INR elevation (lack of vitamin K).
Cholestatic syndromes may be subclassified as either disorders of hepatocytes and microscopic bile ducts (intrahepatic cholestasis) or anatomic obstruction of the macroscopic bile ducts (extrahepatic cholestasis).8 The approach to a patient with cholestasis generally begins with a radiographic study, often a right upper-quadrant ultrasound, to look for dilation of bile ducts within or outside of the liver. Dilation of the bile ducts indicates extrahepatic cholestasis; otherwise, extrahepatic cholestasis is largely excluded, and the next step is to investigate for various causes of intrahepatic cholestasis.
Intrahepatic cholestasis includes a variety of processes that interfere with hepatocyte secretion of bile as well as diseases of the microscopic and macroscopic bile ducts within the liver. Etiologies involving impaired hepatocyte secretion of bile overlap to some extent with hepatocellular diseases as noted previously; such processes include viral hepatitis (especially type A), alcoholic hepatitis, and even cirrhosis. Processes that cause a cholestatic pattern include a variety of drugs (Table 15-2), pregnancy, severe infection (cholestasis of sepsis), and certain nonhepatic neoplasms, especially renal cell carcinoma. Infiltrative processes of the liver produce a primarily cholestatic pattern, and these include granulomatous diseases and amyloidosis. PBC causes inflammatory scarring of the microscopic bile ducts, whereas sclerosing cholangitis is a similar process that may affect microscopic or macroscopic bile ducts. Masses within the liver, including tumors or abscesses, may block the flow of bile as well.
aNote that listings of drugs contain more commonly used agents and are not exhaustive. For any particular patient, potentially causative drugs should be specifically researched in the appropriate databases to determine any hepatotoxic effects, such as the National Library of Medicine database, LiverTox: Livertox.nih.gov/.
Extrahepatic cholestasis involves obstruction of the larger bile ducts both inside and outside the liver. The most common cause is stones in the common bile duct; other causes include obstruction by strictures (after surgery), tumors (of the pancreas, ampulla of Vater, duodenum, or bile ducts), chronic pancreatitis with scarring of the ducts as they pass through the pancreas, and parasitic infections of the ducts. Another cause is primary sclerosing cholangitis (PSC), a disease-causing diffuse inflammation of the bile ducts, often both intrahepatic and extrahepatic. Of note is that PSC is associated with inflammatory bowel disease, especially involving the colon. Some patients with human immunodeficiency virus (HIV) can develop a picture similar to sclerosing cholangitis, referred to as AIDS cholangiopathy. Although previously referred to as surgical cholestasis, extrahepatic cholestasis can often be treated or at least palliated using endoscopic means (eg, dilation of strictures with or without stent placement). Another entity is immunoglobulin G (IgG) 4–related sclerosing cholangitis. This is an autoimmune disease, a variant of autoimmune hepatitis, often with elevated autoimmune markers (antinuclear antibody, abnormal serum protein electrophoresis). It can present with a picture of sclerosing cholangitis or even one mimicking cholangiocarcinoma, but the elevated autoimmune markers, especially elevated levels of IgG4, help make this distinction. Tissue biopsy reveals IgG4, plasma cell infiltrates, and interstitial fibrosis. Patients characteristically respond to glucocorticoids.
Tests Associated with Excretory Liver Function and Cholestasis
Laboratory tests do not distinguish between intrahepatic and extrahepatic cholestasis. This distinction is usually made radiographically. In most instances of extrahepatic cholestasis, a damming effect causes dilation of bile ducts above the obstruction, which can be visualized via computed tomography (CT), magnetic resonance imaging (MRI), or ultrasound. Laboratory abnormalities primarily associated with cholestasis include elevation of ALP, 5′-nucleotidase, γ-glutamyl transpeptidase (GGT), and bilirubin.
Normal range: 33 to 96 units/L (0.56 to 1.63 µkat/L)
Alkaline phosphatase (ALP) refers to a group of isoenzymes whose exact function remains unknown. These enzymes are found in many body tissues, including the liver, bone, small intestine, kidneys, placenta, and leukocytes. In the liver, they are found primarily in the bile canalicular membranes of the liver cells. In adults, most serum ALP comes from the liver and bone (∼80%), with the remainder mostly contributed by the small intestine.
Normal ALP concentrations vary primarily with age. In children and adolescents, elevated ALP concentrations result from bone growth, which may be associated with elevations as high as three times the adult normal range. Similarly, increase during late pregnancy is due to placental ALP.9 In the third trimester, concentrations often double and may remain elevated for 3 weeks postpartum.
The mechanism of hepatic ALP release into the circulation in patients with cholestatic disease remains unclear. Bile accumulation appears to increase hepatocyte synthesis of ALP, which eventually leaks into the bloodstream. ALP concentrations persist until the obstruction is removed and then normalize within 2 to 4 weeks.
Clinically, ALP elevation is associated with cholestatic disorders and, as mentioned previously, does not help to distinguish between intrahepatic and extrahepatic disorders. ALP concentrations more than four times normal suggest a cholestatic disorder, and 75% of patients with primarily cholestatic disorders have ALP concentrations in this range (Table 15-3). Concentrations of three times normal or less are nonspecific and can occur in all types of liver disease. Mild elevations, usually <1.5 times normal, can be seen in healthy patients and are less significant.
Initial Evaluation of Elevated ALP Concentrations in Context of Other Test Results
When faced with an elevated ALP concentration, a clinician must determine whether it is derived from the liver. One approach is to fractionate the ALP isoenzymes using electrophoresis, but this method is expensive and often unavailable. Thus, the approach usually taken is to measure other indicators of cholestatic disease, 5′-nucleotidase, or GGT. If ALP is elevated, an elevated 5′-nucleotidase or GGT indicates that at least part of the elevated ALP is of hepatic origin. Alternatively, a normal 5′-nucleotidase or GGT suggests a nonhepatic cause (Table 15-3).
Nonhepatic causes of elevated ALP include bone disorders (eg, healing fractures, osteomalacia, Paget’s disease, rickets, tumors, osteoporosis, hypervitaminosis D, or vitamin D deficiency as caused by celiac sprue), hyperthyroidism, hyperparathyroidism, sepsis, diabetes mellitus, renal failure, and neoplasms (which may synthesize ALP ectopically, outside tissues that normally contain ALP) (Table 15-4). Some families have inherited elevated concentrations (two to four times normal), usually as an autosomal dominant trait.10 Markedly elevated concentrations (more than four times normal) are generally seen only in cholestasis, Paget’s disease, or infiltrative diseases of the liver. Because of an increase in intestinal ALP, serum ALP concentrations can be falsely elevated in patients with blood type O or B whose blood is drawn 2 to 4 hours after a fatty meal.11 Alkaline phosphatase concentrations can be lowered by several conditions, including hypothyroidism, hypophosphatemia, pernicious anemia, and zinc or magnesium deficiency. Also, ALP may be confounded by a variety of drugs.
Some Nonhepatic Illnesses Associated with Elevated ALP
OTHER DISORDERS AND DRUGS
Anticonvulsant drugs (eg, phenytoin and phenobarbital)
Lithium (bone isoenzymes)
Small bowel obstruction
Pregnancy (third trimester)
Normal range: 0 to 11 units/L (0 to 0.19 µkat/L)
Although 5′-nucleotidase is found in many tissues (including liver, brain, heart, and blood vessels), serum 5′-nucleotidase is elevated most often in patients with hepatic diseases. It has a response profile parallel to ALP and similar utility in differentiating between hepatocellular and cholestatic liver disease. Because it is only elevated in the face of liver disease, the presence of an elevated ALP together with a normal 5′-nucleotidase (or GGTP, see below) suggests that the ALP is elevated secondary to nonhepatic causes.
Normal range: 9 to 58 units/L (0.15 to 0.99 µkat/L)
γ-glutamyl transpeptidase (GGT, also GGTP), a biliary excretory enzyme, can also help determine whether an elevated ALP is of hepatic etiology. Similar to 5′-nucleotidase, it is not elevated in bone disorders, adolescence, or pregnancy. It is rarely elevated in conditions other than liver disease.
Generally, GGT parallels ALP and 5′-nucleotidase levels in liver disease. Additionally, GGT concentrations are usually elevated in patients who abuse alcohol or have alcoholic liver disease. Therefore, this test is potentially useful in differential diagnosis, with a GGT/ALP ratio >2.5 being highly indicative of alcohol abuse.12 With abstinence, GGT concentrations often decrease by 50% within 2 weeks.
Although it is often regarded as the most sensitive test for cholestatic disorders, GGT is unlike 5′-nucleotidase in that GGT lacks specificity. Not all GGT elevations are of hepatic origin. GGT is found in the liver, kidneys, pancreas, spleen, heart, brain, and seminal vesicles. Elevations may occur in pancreatic diseases, myocardial infarction, severe chronic obstructive pulmonary diseases, some renal diseases, systemic lupus erythematosus, hyperthyroidism, certain cancers, rheumatoid arthritis, and diabetes mellitus. GGT may be confounded in patients on a variety of medications, some of which overlap with the medications that confound ALP test results. Thus, elevated GGT (even with concomitant elevated ALP) does not necessarily imply liver injury when 5′-nucleotidase is normal, but rather both elevations in GGT and ALP may be caused by a common confounding medication (eg, phenytoin, barbiturates) or medical condition (eg, myocardial infarction).
Total bilirubin: 0.3 to 1.3 mg/dL (5.1 to 22 µmol/L)
Indirect (unconjugated, insoluble) bilirubin: 0.2 to 0.9 mg/dL (3.4 to 15.2 µmol/L)
Direct (conjugated, water soluble) bilirubin: 0.1 to 0.4 mg/dL (1.7 to 6.8 µmol/L)
Understanding the various laboratory studies of bilirubin requires knowledge of the biochemical pathways for bilirubin production and excretion (Figure 15-3). Bilirubin is a breakdown product of heme pigments, which are large, insoluble organic compounds. Most of the body’s heme pigments are located in erythrocytes (red blood cells), in which they are a component of hemoglobin. Breakdown of erythrocytes releases hemoglobin into the circulation (which is converted to bilirubin, predominantly in the spleen), where it is initially a large lipophilic molecule bound to albumin.
The liver plays a central role in excretion of bilirubin, similar to its role in the metabolism and excretion of a wide variety of lipophilic substances. Prior to excretion, bilirubin must be converted into a form that is water soluble. The liver achieves this by covalently linking it to a water-soluble sugar molecule (glucuronic acid) using an enzyme glucuronyl transferase. The conjugate of bilirubin linked to glucuronic acid is water soluble, so it may then be excreted into the bile and eventually eliminated in the feces. Incidentally, bilirubin and some of its breakdown products are responsible for coloring feces brown (such that with complete obstruction of the bile ducts or cessation of bile synthesis by the liver, the stool takes on a pale color). With progressive cholestasis, there is increased renal excretion of the water-soluble bilirubin, coloring the urine dark brown.
Indirect Versus Direct Bilirubin
The total amount of bilirubin in the serum can be divided into direct and indirect fractions. Bilirubin conjugated to glucuronic acid (water-soluble bilirubin) reacts quickly in the van der Bergh reaction and is thus called direct-reacting or direct bilirubin. Alternatively, unconjugated bilirubin, because it is water insoluble, requires the presence of dissolving agents to be detected by this assay and is thus called indirect-reacting or indirect bilirubin. Although this nomenclature system is slightly awkward, it is the standard terminology used in clinical practice today. Labs generally measure the total bilirubin and the direct bilirubin. Indirect bilirubin may be determined by subtracting the direct from the total bilirubin. Only the water-soluble direct bilirubin can be excreted in the urine; therefore, urine dipsticks only will measure this fraction. In fact, urine dipsticks may be more sensitive than most serum tests for detecting a slight elevation of direct bilirubin.
Elevated bilirubin causes abnormal yellow coloration of the skin and sclera of the eyes (collectively, these symptoms are referred to as jaundice or icterus). Excess carotenes (eg, due to large amounts of carrot consumption) may cause a similar effect on the skin but spare the eyes. Icterus usually becomes visible when total bilirubin concentrations exceed 2 to 4 mg/dL. In infants, extremely elevated concentrations of bilirubin (for example, >20 mg/dL) may have neurotoxic effects on the developing brain, but in adults a direct toxic effect of bilirubin is quite rare.
The first step in evaluating an elevated serum bilirubin is to determine if only the indirect fraction is elevated or if there is involvement of the direct fraction. Given the sequential location of these two molecules within the pathway of bilirubin metabolism, elevated levels of the molecules may have markedly different significance (Table 15-5).
Evaluation of Elevated Bilirubin Concentrations in Context of Other Test Results
Indirect bilirubin is mostly produced by the breakdown of erythrocytes and is removed from the circulation by conversion to direct bilirubin by glucuronyl transferase in the liver. Therefore, elevated levels may result from increased breakdown of red blood cells (hemolysis) or reduced hepatic conversion to direct bilirubin. Patients with primarily unconjugated hyperbilirubinemia (>70% indirect) generally do not have serious liver disease. The most common causes of elevated indirect bilirubin are hemolysis, Gilbert syndrome, Crigler-Najjar syndrome, and various drugs, including probenecid and rifampin. In infants, this can be physiologic (neonatal jaundice), although very high levels may require medical intervention.
Hemolysis refers to increased destruction of erythrocytes, which increases the production of indirect bilirubin and may overwhelm the liver’s ability for conjugation and excretion. However, the liver’s processing mechanisms are intact so that serum bilirubin generally does not rise dramatically (rarely >5 mg/dL). Hemolysis may result from a wide variety of hematologic processes, including sickle cell anemia, spherocytosis, hematomas, mismatched blood transfusions, and intravascular fragmentation of blood cells. Evaluation includes various hematologic tests, as described in further detail in Chapter 16.
Gilbert syndrome is an inherited, benign trait present in 3% to 5% of the population. It is due to reduced production of hepatic glucuronyl transferase enzymes, resulting in intermittent elevation of indirect bilirubin and mild jaundice (increased with fasting, stress, or illness). The primary significance is that it may cause elevation of bilirubin when there is in fact no significant hepatic or hematologic disease. Bilirubin elevation is generally mild, with values <5 mg/dL.
Direct Hyperbilirubinemia (Conjugated, Soluble)
Conjugated hyperbilirubinemia is defined as bilirubinemia with >50% in the direct fraction (although absolute levels of unconjugated bilirubin may also be elevated). In the normal course of bilirubin metabolism, direct bilirubin is synthesized in hepatocytes by conjugating indirect bilirubin and secreted into bile. Therefore, elevated direct bilirubin implies hepatic or biliary tract disease that interferes with secretion of bilirubin from the hepatocytes or clearance of bile from the liver.
Direct hyperbilirubinemia is generally classified as a positive cholestatic liver test, although as discussed earlier, it may be elevated to some extent in hepatocellular processes as well. In cholestatic disease, elevated bilirubin is primarily conjugated, whereas in hepatocellular processes significant increases in both conjugated and unconjugated bilirubin may result. The most reliable method of determining the cause of hyperbilirubinemia considers the magnitude and pattern of abnormalities in the entire liver function panel. It should be noted that direct bilirubin is generally readily cleared by the kidney, such that its levels rarely rise very high, even in severe cholestatic disease if a patient has normal renal function. Very rarely, congenital disorders (eg, Dubin-Johnson and Rotor syndromes) may cause elevations of primarily conjugated bilirubin.
It should be noted that a gray area exists between indirect and direct hyperbilirubinemia. Most authors agree that >50% direct bilirubin indicates direct hyperbilirubinemia whereas <30% direct fraction indicates indirect hyperbilirubinemia. For cases in which the fraction falls between 30% and 50%, other liver tests and hematologic tests may be required to determine the etiology.
Patients with elevated direct bilirubin levels may have some binding of bilirubin to albumin, referred to as δ bilirubin. This explains delayed resolution of jaundice during recovery from acute hepatobiliary diseases; while the “free” bilirubin is rapidly metabolized, the bilirubin linked to albumin is metabolized at a much slower rate. ∆ bilirubin has a half-life of 14 to 21 days, which is similar to albumin.13
As discussed earlier, the liver is a large organ with diverse biochemical roles, which require its cells to be in close communication with the bloodstream. These properties place the hepatocytes at risk for injury due to a variety of processes. Toxin and drug metabolism produce cascades of metabolic byproducts, some of which may damage hepatocytes. Likewise, the liver plays a central role in the body’s biochemical homeostasis, so metabolic disorders tend to involve the liver. Finally, the close relationship of hepatocytes to the blood supply places them at risk for a variety of infectious agents.
Hepatitis is a term that technically refers to a histologic pattern of inflammation of hepatocytes. It may also be used to refer to a clinical syndrome caused by diffuse liver inflammation. The laboratory reflection of hepatitis is a hepatocellular injury pattern, which is marked primarily by elevated aminotransferases.
There are multiple causes of hepatitis. One common type is viral hepatitis, which is classified A, B, C, D (δ hepatitis), or E based on the causative virus. These viruses, and the tests for them, are discussed in detail in the Viral Hepatitis section. Less common viral hepatitis may be caused by the Epstein-Barr virus, herpes virus, or cytomegalovirus.
Hepatitis may also be caused by various medications, and drug-induced hepatitis can be either acute or chronic. Some drugs commonly implicated in cellular hepatotoxicity are listed in Table 15-2. In addition, elevation of aminotransferases has been reported in patients receiving heparin.14 ALT is elevated in up to 60% of these patients, with a mean maximal value of 3.6 times the baseline. A vast number of drugs can cause hepatic injury, especially drugs that are extensively metabolized by the liver. Although numerous drugs may result in aminotransferase elevations, such elevations are usually minor, transient, not associated with symptoms, and of no clinical consequence.
Perhaps the most common cause of abnormal aminotransferases in ambulatory patients is fatty liver.15 Estimates are 30% to 46% of adults in the United States have fatty liver, which can vary from hepatic steatosis (fat in the liver) to nonalcoholic steatohepatitis (NASH), in which the extra fat in the liver is associated with inflammation. It is potentially serious because up to one-fourth of these patients can progress to having cirrhosis. Fatty liver and NASH are mostly related to increased body mass index, but they can also be associated with rapid weight loss or drugs such as tamoxifen, amiodarone, diltiazem, nifedipine, corticosteroids, and petrochemicals. Fatty liver/NASH can be seen in patients with hepatitis C and patients on total parenteral nutrition, and it is associated with hypothyroidism and short bowel syndrome.
It is important to note that although mild hepatic inflammation is often of minimal significance, it may signal the presence of a chronic and serious disease process. Some other causes of hepatic inflammation and injury are listed in Table 15-2.
It is often difficult to determine the exact etiology of hepatic inflammation or hepatitis. A careful history—especially for exposure to drugs, alcohol, or toxins—and detailed physical examination are crucial. Additional laboratory studies are usually necessary to distinguish one form of hepatitis from another (Figure 15-4). Radiologic testing or liver biopsy may be indicated, not only to determine the etiology of the liver disease but also to help determine the indications for (and results of) therapy and prognosis.
Aminotransferases: Aspartate Aminotransferase and Alanine Aminotransferase
AST: 12 to 38 units/L (0.2 to 0.65 µkat/L); ALT: 7 to 41 units/L (0.12 to 0.70 µkat/L) (normal values for either test vary from laboratory to laboratory but tend to be in the range of <30 units/L for men and <20 units/L for women)
The aminotransferases (also known as transaminases) are used to assess hepatocellular injury and include AST (formerly serum glutamic-oxaloacetic transaminase) and ALT (formerly serum glutamic-pyruvic transaminase). These enzymes are primarily located inside hepatocytes, where they assist with various metabolic pathways. They are released into the serum in greater quantities when there is hepatocyte damage, are very sensitive, and may be elevated even with minor levels of hepatocyte damage. However, this renders them relatively nonspecific, and slightly elevated levels may not be clinically significant (particularly in an ill, hospitalized patient who is on many medications and has a variety of active medical problems).
Aminotransferases are often slightly increased in cholestatic liver diseases, but in this situation, they are generally overshadowed by a greater elevation of cholestatic liver tests (ie, ALP and total bilirubin to produce a predominantly cholestatic pattern of liver tests). If both aminotransferases and cholestatic tests are elevated in a similar pattern, it suggests a severe hepatocellular process, which interferes with bile secretion at the level of the hepatocytes. Finally, it should be noted that aminotransferases may rise into the thousands within 24 to 48 hours after common bile duct obstruction, after which they decline rapidly. This is one instance in which a cholestatic process may transiently cause a hepatocellular injury LFT profile.
Both AST and ALT have half-lives of 17 and 47 hours, respectively, so they reflect active hepatocyte damage and not, for example, damage to hepatocytes that occurred weeks, months, or years previously. This may lead to some counterintuitive relationships between aminotransferase levels and the overall state of the liver. For example, a drop in aminotransferase levels in the setting of acute massive (fulminant) hepatitis may reflect a depletion of viable hepatocytes with poor prognosis. Extremely high concentrations (>1,000 units/L) are usually associated with acute viral hepatitis, severe drug or toxic reactions, or ischemic hepatitis (inadequate blood flow to the liver). Lesser elevations are caused by a vast number of hepatic insults and are less specific.
The ratio of AST to ALT may be of value in diagnosing alcoholic hepatitis, in which the AST is generally at least twice the ALT, and the AST is rarely >300 units/L. In alcoholic liver disease, this is due, in part to a deficiency of pyridoxal 5′-phosphate, which favors production of ALT over AST.16 Alcoholic liver disease is also suggested by an elevation in GGT, as previously reviewed.
AST is not solely located in hepatocytes but rather is also found in cardiac muscle, skeletal muscle, kidneys, brain, lungs, intestines, and erythrocytes. Consequently, AST may be elevated due to a variety of situations, including musculoskeletal diseases (eg, muscular dystrophy, dermatomyositis, heavy exercise, trichinosis, gangrene, and muscle damage secondary to hypothyroidism), myocardial infarction, renal infarction or failure, brain trauma or cerebral infarction, hemolysis, pulmonary embolism, necrotic tumors, burns, and celiac sprue. ALT is more localized to the liver than AST, so it is more specific to liver injury. Elevation of AST without elevation of the ALT or other liver test abnormality suggests cardiac or muscle disease. A muscular origin of aminotransferases may also be indicated by increases in aminotransferases >300 International Units/L with concomitant increases in serum creatine kinase activity.
Measurement of AST may be affected by a bewildering variety of medications. Almost any prescription drug (as well as various herbal compounds and illegal drugs) can cause an elevation of aminotransferases, and the significance of these elevations is often unclear. Furthermore, the in vitro assay may be confounded by a variety of factors, including uremia, hyperlipidemia, and hemolysis.17 False elevations in the in vitro test may also be seen in patients on acetaminophen, levodopa, methyldopa, tolbutamide, para-aminosalicylic acid, or erythromycin.
Other factors may interfere with the test’s accuracy. Levels may be elevated to two to three times normal by vigorous exercise in male patients and decreased to about half following dialysis. Complexing of AST with immunoglobulin (known as macro-AST) may occasionally produce a clinically irrelevant elevation of AST.18 Testing for macro-AST is not a clinical laboratory test used in practice. Given the array of factors that can cause an abnormal result, unexplained false-positive results often occur. In healthy individuals, an isolated elevated ALT returns to normal in repeat studies one-half to one-third of the time. For this reason, prior to an evaluation of mildly elevated aminotransferases in low-risk healthy patients, a practitioner should check for an elevation of more than one test (ie, both AST and ALT) or repeated elevations of a single test.
TESTS ASSOCIATED WITH DETOXIFICATION
Hepatic encephalopathy refers to a potentially reversible diffuse metabolic dysfunction of the brain that may occur in acute or chronic liver failure.19 Clinically, it ranges from subtle changes in personality to coma and death. The etiology of hepatic encephalopathy remains controversial. Many theories ascribe a major role to ammonia. Most ammonia enters the portal circulation from the intestines, where it is formed by bacterial catabolism of protein within the gut lumen as well as conversion of serum glutamine into ammonia by enterocytes of the small intestine. Normally, the liver removes >90% of this ammonia via first-pass metabolism before it can enter the systemic circulation.20 In liver failure, ammonia, along with possibly other toxic substances, may avoid this first-pass metabolism and gain immediate access to the brain, where it has a variety of toxic effects. While the exact role of ammonia in terms of hepatic encephalopathy is not clear, it is of interest that current treatment seems focused on lowering serum ammonia levels.
Normal range: 19 to 60 mcg/dL (11 to 35 µmol/L)
Ammonia levels do not correlate well with hepatic encephalopathy in the setting of chronic liver failure (ie, patients with cirrhosis). This is likely because hepatic encephalopathy also involves an increase in the permeability of the blood–brain barrier to ammonia. There is a large overlap between ammonia levels in patients with and without hepatic encephalopathy among patients with chronic liver disease, making it a poor test in this situation.21 Although a very high ammonia level (ie, >250 mcg/dL) is suggestive of hepatic encephalopathy, most patients with cirrhosis suspected of having encephalopathy have normal or slightly elevated ammonia levels, which adds little diagnostic information. Generally, hepatic encephalopathy is a clinical diagnosis based on history, physical exam, and exclusion of other possibilities. Psychometric testing is becoming increasingly available to assist in confirming this diagnosis. Recent articles have questioned the value of checking ammonia levels in terms of their utility in guiding therapy.22
Some recent studies have suggested that ammonia levels may have more significance in the setting of acute liver failure (eg, due to overwhelming infection of the liver by viral hepatitis). In these patients, the degree of ammonia elevation correlates with the severity of hepatic encephalopathy and the likelihood of death, and it may be a useful marker for predicting which patients may require emergent liver transplant.23
Ammonia concentration may also be elevated in patients with Reye syndrome, inborn disorders of the urea cycle, various medications (most notably valproic acid), impaired renal function, ureterosigmoidostomy, or urinary tract infections with bacteria that convert urea to ammonia. In patients with cirrhosis or mild liver disease, elevated ammonia and hepatic encephalopathy may be precipitated by such factors as increased dietary protein, GI bleeding, constipation, and H pylori infection. Patients with vascular shunts or bypass procedures in which blood flow is directed from the portal circulation directly into the systemic circulation (as in transjugular intrahepatic portosystemic shunt) are more likely to develop hepatic encephalopathy.
The onset of acute viral hepatitis may be dramatic and present as an overwhelming infection, or it may pass unnoticed by the patient. In the usual prodromal period, the patient often has a nonspecific flu-like illness that may include nausea, vomiting, fatigue, or malaise. This period may be followed by clinical hepatitis with jaundice. During this time, the most abnormal laboratory results are usually the aminotransferases, which can be in the thousands. Bilirubin may be quite elevated, while ALP only mildly so.
The major types of viral hepatitis are reviewed here, but they are often clinically indistinguishable. Thus, serologic studies of antibodies, molecular assays to detect viral genetic material, and knowledge of the epidemiology and risk factors for these different viruses (Table 15-6) are central to diagnosis.
Groups at Higher Risk of Infection by Various Hepatitis Viruses
Hepatitis A virus
Persons in contact with infected persons
Daycare workers and attendees
Travelers to countries with high rate of hepatitis A infections
Men who have sex with men
IV drug users
Hepatitis B virus
Persons in contact with infected persons
Unvaccinated healthcare professionals and morticians
Recipients of transfusion or organ transplant before July 1992
Children born to HCV-positive mothers
Hepatitis D virus
Only individuals with chronic HBV infection
Hepatitis E virus
Travelers to Latin America, Egypt, India, and Pakistan
Persons in contact with infected persons
*Even one isolated incident of injection drug use can lead to Hepatitis C.
Type A Hepatitis
Hepatitis A virus (HAV) is spread primarily by the fecal–oral route by contaminated food or water or by person-to-person contact. It has an incubation period of 3 to 5 weeks with a several-day prodrome (preicteric phase) before the onset of jaundice and malaise, or the icteric phase. The icteric phase generally lasts 1 to 3 weeks, although prolonged courses do occur. Hepatitis A is responsible for about 50% of acute hepatitis in the United States (more than all other hepatotropic viruses combined), generally due to person-to-person contact within community-wide outbreaks. Between 2016 and 2018, reports of hepatitis A infections in the United States increased by 294% compared with 2013 to 2015; this increase reflects outbreaks involving individuals who report drug use or homelessness, men who have sex with men, and contaminated food items.24
Unlike types B, C, and D hepatitis virus, HAV does not cause chronic disease, and recovery usually occurs within 1 month. Many patients who get type A hepatitis never become clinically ill. Perhaps 10% of all patients become symptomatic, and only 10% of those patients become jaundiced. Fulminant hepatic failure occurs in <1% of cases. Most patients have a full recovery, but there is a substantial mortality risk in elderly patients and very young patients, in patients with chronic hepatitis B or C, and in patients with chronic liver disease of other etiologies.
A vaccine for HAV is available. It is recommended for those from or traveling to endemic regions (ie, Central and South America), men who have sex with men, users of street drugs, those with occupational exposure, patients requiring clotting factor concentrates, and patients with chronic liver diseases. This vaccine is increasingly being recommended as a universal vaccine for pediatric patients. Although this vaccine is generally preferred for postexposure prophylaxis, use of immunoglobulin should be considered in the very young (<12 months) or patients who cannot receive the vaccine.
Presently, the only two tests available to measure antibodies to HAV are immunoglobulin M (IgM) or total (all isotypes of) antibody. Detection of IgM is the more clinically relevant test as it reveals acute or recent infection. These antibodies are present at the onset of jaundice and decline within 12 (but usually 6) months. Total antibody, which is comprised of antibody of all isotypes against HAV, indicates present or previous infection or immunization (Figure 15-5).
Type B Hepatitis
Hepatitis B virus (HBV) is a DNA virus spread by bodily fluids, most commonly as a sexually transmitted disease, but also via contaminated needles (as with parenteral drug abuse or needle stick accidents), shared razor blades or toothbrushes, nonsterile tattooing or body piercing, blood products, or vertical transmission (transmission from mother to child, generally at birth). This disease is 50 to 100 times more contagious than HIV. The incubation period of HBV varies from 2 to 4 months, much longer than that of HAV. Geographically, there is a markedly increased prevalence of hepatitis B in Southeast Asia, China, and sub-Saharan Africa, with 10% to 20% of the populations being hepatitis B carriers. In contrast, the incidence of hepatitis B carriers in the United States is approximately 0.4%.
The clinical illness is generally mild and self-limited but can be quite severe. Unfortunately, up to 5% of infected adults and 90% of infected neonates develop a chronic illness. Chronic HBV infection is often mild but may progress to cirrhosis, liver failure, or hepatocellular carcinoma, thereby contributing to premature death in 15% to 25% of cases.
Viral Antigens and Their Antibodies
Three HBV antigens and antibody systems are relevant to diagnosis and management: surface antigen (HBsAg), core antigen (HBcAg), and e antigen (HBeAg). HBsAg is present on the outer surface of the virus, and neutralizing hepatitis B surface antibodies (anti-HBs) directed against this protein are central to natural and vaccine-induced immunity (Figure 15-6). Neither HBcAg nor HBeAg are on the surface of the virion, and thus antibodies against these antigens are not protective. Nevertheless, antibodies are directed against these proteins and may serve as markers of infection. Of these antigens, only HBsAg and HBeAg can be detected in the serum by conventional techniques. HBsAg is detected for a greater window of time during infection and reveals active infection. Detection of HBeAg indicates large amounts of circulating HBV; these patients are 5 to 10 times more likely to transmit the virus than are HBeAg-negative persons.
In response to infection with HBV, the body may produce anti-HBs, hepatitis B core antibody (anti-HBc), and hepatitis B e-antibody (anti-HBe). All of these antibodies can be detected in clinical laboratories, and in the case of anti-HBcAg, separate tests are available to detect IgM or total antibody (all isotypes). Anti-HBs are associated with resolved type B hepatitis or patients who have responded to vaccination for HBV. Anti-HBc is a bit more challenging to interpret, as it can be seen in acute type B hepatitis, after recovery from type B hepatitis (often in concert with anti-HBs), and in chronic infection (often with HBsAg and HBeAg), and there can be false-positive results as well. As shown in Table 15-7 and Figure 15-7, levels of antigens and antibodies show complex patterns in the course of HBV infection and thus can yield considerable information about the infection’s course and chronology.
Interpretation of Common Hepatitis B Serological Test Results
Acute infection or chronic hepatitis B
Resolving hepatitis B or previous infection
Resolving or recovered hepatitis B or patient after vaccination
In addition to serological tests, sensitive molecular assays may be used to detect HBV DNA, revealing active viral replication in either acute or chronic infection. These assays may be useful for early detection, as in screening blood donors, because DNA is detectible an average of 25 days before seroconversion. Additionally, some assays allow the quantification of serum viral load, which may be used in the decision to treat and, subsequently, monitor therapy. Presently, eight genotypes of HBV have been identified, which can be of real value in terms of determining appropriate therapy for chronic infection. For example, genotype A—most prevalent in the United States—seems to respond better to interferon than the others, and patients with this genotype might benefit from starting with interferon as opposed to the oral agents available. Genotype C is more prevalent in Asia. For the details of these assays (PCR, RNA:DNA hybrid capture assay, nucleic acid cross-linking assay, and branched DNA assay), refer to a review by Pawlotsky et al.25
Acute Type B Hepatitis
HBsAg titers usually develop within 4 to 12 weeks of infection and may be seen even before elevation of aminotransferases or clinical symptoms (Figure 15-7). Subsequently, HBsAg levels decline as anti-HBs titers develop, which indicates resolution of the acute symptomatic infection and development of immunity. In between the decline of HBsAg and the rise of anti-HBs, there is often a window when neither is present during which time anti-HBc may be used to diagnose infection. IgM anti-HBc may be used to reveal acute infection as opposed to a flare of chronic HBV.
Chronic Type B Hepatitis
The development of chronic hepatitis B is suggested by the persistence of elevated LFTs (aminotransferases) and is supported by persistence of HBsAg for >6 months. Persistence of HBeAg also suggests chronic infection, but some chronically infected patients produce anti-HBe and, subsequently, clear HBeAg well after the acute phase is over (late seroconversion; Figure 15-8). Clearance of HBeAg is associated with a decrease in viral DNA and some degree of remission in chronic hepatitis B. However, this can be confusing because HBeAg is a precore protein, and in patients infected with certain mutations developed during the course of the disease (precore and core promoter), HBeAg may not be produced. Yet even in the face of anti-HBe, there may be active disease with ongoing fibrosis and development of cirrhosis. Although chronically infected individuals usually lack anti-HBs, in some cases low levels of nonneutralizing antibodies may be present. Additionally, low levels of IgM anti-HBc may persist.
Hepatitis B Vaccine
The HBV vaccine consists of recombinant HBsAg, which, although not infectious, stimulates the production of protective anti-HBs. Generally, this is a safe vaccine, with efficacy of >90%. Presently, it is recommended as a standard vaccine for neonates. The hepatitis B vaccine is administered in a total of three doses, given at 0, 1, and 6 months. In those who were not vaccinated at birth, it is indicated for people at high risk of acquiring type B hepatitis or its complications including neonates of mothers with hepatitis B, men who have sex with men, injection drug abusers, dialysis patients, healthcare workers, patients with HIV, family and household contacts of patients with type B hepatitis, sexually active people with multiple partners, and patients with chronic liver disease. It should also be considered in patients about to undergo chemotherapy or other forms of immunosuppression. More recent efforts, especially in endemic countries, are leading to this being accepted as a universal vaccine. This vaccine, for example, is often required for students in the United States before entering the public school system.
A vaccine product directed against both HAV and HBV is available. In analyzing serologic data, successful vaccination may be distinguished from previous infection by the presence of anti-HBs and absence of antibodies against other antigens (eg, HBcAg, HBeAg). Testing for antibodies after vaccination is not generally recommended, with exceptions including healthcare workers, dialysis patients, and the spouses or sexual partners of infected patients. Although some patients fail to develop antibodies for a number of reasons, including anergy, these patients should be evaluated for the possibility of occult chronic HBV infection if antibody tests are negative after the second vaccine series. The vaccine has a prolonged duration of action. Routine booster injections are not recommended except, perhaps, for dialysis patients when their titers of anti-HBs are <10 International Units/L.
Type C Hepatitis
Hepatitis C virus (HCV) is an RNA virus mainly spread parenterally, although it may also be transmitted vertically and sexually.26 Although 70% to 80% of acute infections are asymptomatic, 70% to 80% of patients develop chronic disease. Given the mildness of the acute attack and the tendency to develop into chronic hepatitis, it is understandable why many patients with this disease first present decades later with cirrhosis or, more commonly, chronic elevations of aminotransferases. Because chronic HCV infection is often asymptomatic and LFT results may be normal or intermittently elevated, it is recommended that patients at high risk for HCV be screened appropriately. Patients for whom screening would be appropriate include those born in the United States between 1945 and 1965, patients with a history of illegal drug use. Additionally, patients who received clotting factors before 1987 or blood products or organ transplants before July 1992, are HIV positive, have a history of hemodialysis, or have evidence of liver disease (elevated ALT) should be screened. These guidelines are rapidly changing. Presently, the U.S. Preventive Services Task Force recommends universal screening for everyone between the ages of 18 and 79 years.
Acute hepatitis C is often asymptomatic, and when symptoms are present, they are mild. Diagnosis of acute hepatitis C, however, is important as evidence suggests that prompt treatment with antiviral medications can prevent progression to chronic hepatitis C in most cases.
In chronic hepatitis C infection, the LFT results are usually minimally elevated, with ALT and AST values commonly in the 60 to 100 International Units/L range. These values can fluctuate and occasionally return to normal for a year or more, only to rebound when next checked. The primary clinical concern in chronic HCV is that if untreated, within 20 years 20% to 30% of patients develop cirrhosis and 1% to 5% develop hepatocellular carcinoma.
The first screening test used is often an enzyme-linked immunosorbent assay (ELISA) assay for anti-HCV, which detects antibodies against a cocktail of HCV antigens. Positive test results can be seen in patients who have passively acquired these antibodies (but not the infection), as a result of blood transfusions, or as children of mothers with hepatitis C. Because of possible cross-reactivity with one of the antigens in the assay, this test has a considerable false-positive rate, and thus positive results need to be confirmed with a more specific assay. One such assay is the recombinant immunoblot assay, which is similar to ELISA in principle, but tests antibody reactivity to a panel of antigens individually. Binding to two or more antigens is considered a positive test. Binding to one antigen is considered indeterminate. Presently the approach to a positive ELISA is to skip the recombinant immunoblot assay and go directly to the reverse transcriptase polymerase chain reaction (RT-PCR) assay.
Qualitative RT-PCR, often referred to as just PCR, detects viral RNA in the blood. It is a sensitive assay that may be used in the diagnosis and subsequent management of hepatitis C. RT-PCR has several advantages compared with serologic tests. It can detect HCV within 1 to 2 weeks of exposure and weeks before seroconversion, presentation of symptoms, or the elevation of LFTs. This may be useful because seroconversion only has occurred in 70% to 80% of patients at the onset of symptoms, and it may never occur in immunosuppressed patients. Additionally, there is evidence suggesting that treating acute hepatitis C may be of value. Some immunocompromised patients with hepatitis C (as described previously) may have false-negative ELISA studies, and thus RT-PCR is recommended for consideration in patients with hepatitis or chronic liver disease who are immunosuppressed. Furthermore, unlike serologic assays, RT-PCR is not confounded by passively acquired antibodies that may be present in uninfected infants or recipients of blood products, and RT-PCR can distinguish between resolved and chronic infection.
Once a diagnosis of HCV infection is established, various quantitative molecular assays that monitor viral load may be useful in following viral titers during treatment or assessing the likelihood of response to therapy. A major consideration with these tests is that the methodology is not yet standardized, and there is laboratory-to-laboratory variability. These tests are not preferred for initial diagnosis because they are less sensitive than qualitative RT-PCR. They include a quantitative PCR assay and a branched-chain DNA assay (for more information, see Pawlotsky et al.25). Presently, most laboratories report HCV PCR measurements in International Units/milliliter, with pretreatment levels often in the millions.
There are at least six major genotypes of the type C virus and multiple subtypes. Viral genotype determination is useful because genotype may help direct the antiviral regimen needed, length of therapy, as well as predict the likelihood of response to treatment. Recent release of several new oral antiviral agents has improved treatment in terms of being well tolerated by the patients and yielding eradication rates >90%. Length of treatment may vary depending not only on genotype but also on presence of cirrhosis and previous exposure to other medications. Genotype determination may be done via direct sequencing or hybridization of PCR amplification products.
Type D Hepatitis
Hepatitis D virus (HDV) is caused by a defective virus that requires the presence of HBsAg to cause infection. Therefore, people only can contract type D hepatitis concomitantly with HBV infection (coinfection) or if chronically infected with HBV (superinfection). Coinfection presents as an acute infection that may be more severe than HBV infection alone. Alternatively, the picture of superinfection is that of a patient with known or unknown chronic HBV who develops an acute flare with worsening liver function and increases in HBsAg. Acute coinfection is usually self-limited with rare development of chronic hepatitis, while superinfection becomes chronic in >75% of cases and increases the risk of negative sequelae, such as cirrhosis. Transmission of HDV is generally by parenteral routes, although no obvious cause can be determined in some cases.
Testing for HDV is usually only indicated in known cases of HBV infection. The single, widely available assay detects anti-HDV antibodies of all isotypes (Figure 15-9). This test is unable to distinguish between acute, chronic, or resolved infection and lacks sensitivity because only about 38% of infected patients have detectible anti-HDV within the first 2 weeks of illness. Because seroconversion may occur as late as 3 months after infection, testing may be repeated if the clinical picture suggests HDV. Tests are also available for HDV RNA, and stains are available to assess the D antigen in hepatocytes.
Type E Hepatitis
Hepatitis E virus (HEV) is generally similar to hepatitis A. It is a hardy, protein-coated RNA virus that is spread by the fecal–oral route, often by contaminated food or water. Like HAV, HEV causes an acute illness that is generally self-limited. HEV is endemic in parts of Asia and has become increasingly detected in the United States. Unlike HAV, HEV is notable for a predilection for causing life-threatening illness in women who are in their third trimester of pregnancy. Recently, testing for antibodies to hepatitis E has become available, including HEVAg or hepatitis E antigen. Work is underway to develop a vaccine for hepatitis E.
PRIMARY BILIARY CHOLANGITIS
Primary biliary cholangitis (PBC), previously called primary biliary cirrhosis, is a chronic disease involving progressive destruction of small intrahepatic bile ducts leading to cholestasis and progressive fibrosis over a period of decades. Ultimately, it can progress to cirrhosis and liver failure, necessitating transplantation.27 Ninety percent of affected individuals are women, with onset occurring in adulthood. The etiology of the disease is unknown, although it seems to involve an autoimmune component and is associated with a variety of autoimmune disorders, including Sjögren’s syndrome, rheumatoid arthritis, and scleroderma, and thyroid diseases. The initial symptoms of the disease are often those of progressive cholestasis with fatigue, pruritus, jaundice, and deficiencies in fat-soluble vitamins.
The most useful laboratory test in diagnosing PBC is the detection of antimitochondrial antibodies (AMA), with a sensitivity of 95%. This assay is also highly specific, although patients with autoimmune and drug-induced hepatitis occasionally have low antibody titers. PBC usually presents with a predominantly cholestatic laboratory picture, initially with an elevated ALP and GGT, and later, with an elevated total bilirubin. Aminotransferases tend to be minimally elevated or normal (Minicase 1).
Hemochromatosis is an iron overload state involving the liver and other organs. If left untreated, hemochromatosis can lead to cirrhosis, cardiac failure, diabetes, and hepatocellular carcinoma.28 Its presentation is often subtle, and most cases are discovered either in patients undergoing evaluation of abnormal aminotransferases or presenting with a positive family history of hemochromatosis. Iron overload can be either by a primary or secondary disorder. Hereditary hemochromatosis (also referred to as classic or primary hemochromatosis) is inherited in an autosomal recessive fashion and involves dysregulated handling of iron absorption from the GI tract. Up to 90% of affected individuals have inherited two alleles carrying the mutant C282Y genotype on chromosome 6. Persons of northern European descent have the highest risk, with a greater likelihood in men. Secondary hemochromatosis is generally the result of iatrogenic iron overload from repeated blood transfusions used as therapy for disorders such as thalassemias, sideroblastic anemias, myelodysplastic syndromes, and congenital dyserythropoietic anemias.29
Hemochromatosis remains an underdiagnosed disease entity. Many patients report nonspecific symptoms leading to a delay in diagnosis and treatment for up to several years. The classically reported clinical manifestations of hemochromatosis included the triad of bronze skin, diabetes, and cirrhosis but were infrequent at the time of disease diagnosis. Now more commonly, patients experience malaise, fatigue, arthralgias, hepatomegaly, and elevated aminotransferase levels when diagnosis is confirmed.
Diagnosis typically begins with laboratory assessment of serum ferritin and transferrin iron saturation levels in patients found to have chronically elevated liver enzymes and clinical suspicion of hemochromatosis.30 A transferrin iron saturation level of >60% in men or 50% in women may suggest this, although the American Association for the Study of Liver Diseases guidelines suggests 45% as a cutoff.31 Ferritin levels tend to be elevated as well, >200 ng/mL in men and 150 ng/mL in women. Hemochromatosis gene testing can then be performed on these patients or individuals at risk for hereditary hemochromatosis based on family history. This diagnosis can be suggested in patients who are homozygous for the C282Y gene or compound heterozygote with a copy of the C282Y gene and a copy of the H63D gene. Early diagnosis of hereditary hemochromatosis is important so that therapy can be started before end organ involvement is evident and is associated with improved outcomes.32 Therapeutic phlebotomies to decrease serum ferritin levels may result in a normal life expectancy. Management of secondary hemochromatosis is usually through chelation therapy, but life expectancy may be shorter and related to the need for continued transfusion therapy to treat the primary disorder (Minicases 2 through 11).
Cholestasis in a Middle-Aged Woman
Gwen V., a 52-year-old woman, presents for her routine annual medical examination. She has no new medical complaints. In the past, she was diagnosed with osteoporosis and started on alendronate as well as supplemental vitamin D. She denies alcohol use, illicit drug use, or use of other vitamins or herbal supplements. Her physical examination is entirely normal. Routine laboratory evaluation includes a normal CBC, lipid profile, and renal function. Her liver profile is abnormal, with an elevated ALP of 330 International Units/L. Her AST, ALT, and bilirubin are normal.
An ultrasound of her liver and biliary system is normal. Additional bloodwork shows that her GGT is abnormally elevated at 562 International Units/L. Additional workup demonstrates negative serologies for viral hepatitis, negative ANA, and ASM. Her AMA titer is positive at 1:280. She is told she has primary biliary cirrhosis, needs a liver biopsy, and seeks another opinion.
QUESTION: What disease does she have, and how do we diagnose her? Does she need a liver biopsy?
DISCUSSION: Gwen V. has a cholestatic picture with elevations in ALP and GGTP. Her negative ultrasound helps exclude biliary obstruction. Her positive AMA is a further clue to her diagnosis. Prior to 2014, the diagnostic term was indeed primary biliary cirrhosis. This was an unfortunate term because many of these patients do not have cirrhosis at all. Currently, the correct diagnostic term is primary biliary cholangitis (PBC), which is classified as an autoimmune disease of the liver. Over the course of decades there can be continued inflammation of the small bile ducts in the liver, leading to scarring and ultimately cirrhosis. The disease is much more common in women and is often associated with other autoimmune diseases, especially thyroid disease.
Diagnosis requires two out of the three criteria:
Cholestatic liver tests
Abnormal serum AMA over 1:40
Characteristic findings on liver biopsy
Thus, our patient does not need a liver biopsy because she meets the criteria for PBC. Management would include treatment with ursodiol and following up with her lab results. If her ALP remains elevated, a newer treatment with obeticholic acid might be considered. Patients with PBC may have a higher incidence of osteoporosis, as our patient does. Additionally, lipids may be abnormal.
Case of a Prolonged International Normalized Ratio and Low Serum Albumin
Jane M., a 50-year-old woman, presents to her physician with reports of increasing fatigue and a 20-lb weight loss over the past 4 months. Initial evaluation shows an albumin of 2 g/dL and an INR of 2.3. Jane M. is referred for evaluation of possible cirrhosis. On further questioning, she denies any history of hepatitis, exposure to hepatotoxins, alcohol use, family history of liver disease, or liver disease.
Jane M.’s physical examination does not suggest liver disease; there is no evidence of ascites, palmar erythema, asterixis, hepatomegaly, splenomegaly, or spider angiomata. It is noted that she has pedal edema. Liver function studies are otherwise normal: ALT 12 International Units/L, AST 20 International Units/L, total bilirubin 1 mg/dL, and ALP 56 International Units/L.
An IM dose of vitamin K 10 mg corrects the INR within 24 hours. Workup shows that Jane M. has malabsorption due to sprue, a disease of the small bowel. With proper dietary management, her symptoms resolve and she gains weight. At a follow-up visit 3 weeks later, her albumin concentration is 3.7 g/dL and her edema has resolved.
QUESTION: Why did Jane M. develop a low albumin and a prolonged PT? What caused her pedal edema?
DISCUSSION: This case demonstrates that although low albumin and a prolonged PT suggest advanced liver disease, other causes need to be considered. Administration of vitamin K promptly corrected Jane M.’s INR, suggesting malabsorption of vitamin K. If she had cirrhosis, her PT would not have corrected with the vitamin K. Similarly, her hypoalbuminemia was not due to her liver’s inability to synthesize albumin but to the malabsorptive disorder that was interfering with protein absorption. Therefore, Jane M. had a low albumin and elevated INR in the absence of liver disease. Her pedal edema was due to hypoalbuminemia secondary to malabsorption.
Pancreatitis refers to inflammation of the pancreas (either acute or chronic) and is the most common disease associated with this gland.33 Although there are multiple causes of pancreatitis, the clinical presentation is often the same. Acute pancreatitis generally presents with severe midepigastric abdominal pain developing over an hour, often radiating to the back. The pain tends to be continuous and can last for several days.
This condition is often associated with nausea and vomiting; in severe cases, fever, ileus, and hypotension can occur. Ultimately, there can be progressive anemia, hypocalcemia, hypoglycemia, hypoxia, renal failure, systemic inflammatory response syndrome (SIRS), and death. Clinicians face the challenge of rapidly establishing this diagnosis, because many conditions (eg, ulcers, biliary disease, myocardial infarction, and intestinal ischemia or perforation) can present in a similar manner.
Jaundice Caused by Oral Contraceptives
Amber S., a 16-year-old girl, is found by her pediatrician to be slightly jaundiced during a routine school physical. She denies any history of liver disease, abdominal pain, illicit drug abuse, alcohol use, or abdominal trauma. Laboratory evaluation shows a moderately elevated bilirubin of 2.3 mg/dL along with ALP and GGT concentrations about four times normal. Her AST is 23 International Units/L.
Amber S. denies being on any medications (except for vitamins) or being exposed to toxins. Nothing suggests the possibility of a neoplastic or infectious process (temperature of 98.9°F and WBC count of 7.5 × 103 cells/mm3). Ultrasound of the liver and biliary system is normal with no evidence of biliary dilation.
Her parents take her to a pediatric hepatologist. After much discussion (and threat of a liver biopsy), Amber S. tearfully reveals that she went to a local family planning clinic and is using birth control pills.
QUESTION: How might oral contraceptives cause a cholestatic picture? What is the importance of the ultrasound? What is the usual outcome of patients who develop jaundice while taking oral contraceptives?
DISCUSSION: This case demonstrates that oral contraceptives, primarily because of their estrogen content, can cause alterations in cholestatic test results (manifested by an elevated bilirubin, GGT, and ALP) with relatively normal aminotransferases. The ultrasound helps to distinguish between intrahepatic and extrahepatic cholestasis. The absence of biliary dilation suggests intrahepatic cholestasis. The normal AST suggests that jaundice is not due to hepatitis.
Cholestasis from oral contraceptives is generally benign and reverses promptly when the medication is withdrawn. Patients often omit mentioning use of birth control pills.
Abnormal Liver Function Tests
Dana D., a 36-year-old executive, is referred to a prominent medical center for a second opinion. Her physician finds an elevated AST of 180 International Units/L on a routine screening exam. Dana D. has no symptoms; her physical examination has been normal, without any signs of liver disease or hepatomegaly.
Additional studies show an ALT of 60 International Units/L, a markedly elevated GGT of 380 International Units/L, and a minimally elevated ALP of 91 International Units/L. Her WBC count is elevated at 20 × 103 cells/mm3. After much discussion, she reveals that she has been drinking 1 pint of vodka a day.
Dana D. enrolls in Alcoholics Anonymous and stops drinking. Three months later, her test results are normal: ALT 28 International Units/L, GGT 54 International Units/L, and ALP 54 International Units/L.
QUESTION: What findings suggest alcoholic liver disease? Why did all of Dana D.’s laboratory test results return to normal? What else might have happened in this situation?
DISCUSSION: This case demonstrates several aspects of alcoholic liver disease. The diagnosis is suggested by an elevated AST out of proportion to the ALT (generally an AST/ALT ratio of ≥2), as well as by a markedly elevated GGT with a normal (or virtually so) ALP. AST and ALT levels generally are <300. An elevated mean corpuscular volume (MCV), if present, also would support this diagnosis. Patients with alcoholic liver disease may have markedly elevated WBC counts.
Alcoholic liver disease tends to have several different stages. The earliest manifestation may be just a “fatty liver,” which is generally reversible with cessation of alcohol intake. Alcoholic hepatitis and cirrhosis can follow with continued excessive alcohol intake. Unfortunately, alcoholic cirrhosis can develop without any warning signs. If Dana D. had alcoholic cirrhosis, stopping alcohol consumption probably would not have significantly altered her abnormal test results.
Clinicians should remember that a patient does not need to be an “obvious” alcoholic to develop alcoholic cirrhosis. Women are more susceptible to the hepatotoxic effects of alcohol than men, and as few as two or three drinks a day can cause significant liver disease in susceptible persons, this being due to differences in alcohol metabolism. Of note, 12 oz of beer, 5 oz of wine, and 1.5 oz of “spirits” all have about 14 g of alcohol and thus are equivalent in terms of risk of alcoholic liver disease.
A Jaundiced College Student
Jacob N., a 19-year-old college student, anxiously reports to the infirmary when his girlfriend notices that he has become yellow. He feels well and has a normal physical examination. On discussion, he indicates that he has recently embarked on a rigorous crash diet in anticipation of winter break in Florida.
The evaluation shows an elevated total bilirubin of 4.8 mg/dL, with a direct bilirubin of 0.48 mg/dL. The absence of hemolysis is established by microscopic examination of a blood smear, normal reticulocyte count, and lactate dehydrogenase (LDH), which is 112 International Units/L. Jacob N.’s other LFT results are normal: ALT 21 International Units/L and ALP 76 International Units/L.
QUESTION: What was the most likely cause of Jacob N.’s signs and symptoms? How should his condition be managed? What is his prognosis?
DISCUSSION: Elevated bilirubin concentrations do not necessarily indicate severe liver disease. In this case, the unconjugated bilirubin was substantially elevated. The normal ALT and ALP rule out hepatocellular and cholestatic liver diseases. If done, AST would have been normal. The normal LDH, red blood cell microscopic exam, and reticulocyte count rule out hemolysis as a cause of the elevated unconjugated bilirubin. The normal LDH is also consistent with a lack of intrinsic liver disease.
Jacob N. should be reassured that he has Gilbert syndrome and might become somewhat jaundiced with fasting or acute or chronic illness. Gilbert syndrome is not associated with any symptoms, is totally benign, and requires no treatment. When a patient has an elevated bilirubin, a practitioner should always obtain LFTs before providing a diagnosis or performing unnecessary tests.
Stephen F., a 47-year-old man with alcoholism, is admitted to a hospital after being found on a park bench surrounded by empty beer bottles. Known to have cirrhosis, Stephen F. is thought to be showing signs of hepatic encephalopathy as he slowly lapses into a deep coma over the first 4 days of hospitalization. His physical examination is significant in that he has hepatomegaly and splenomegaly.
Laboratory evaluation shows a negative urine drug screen for central nervous system (CNS) depressants with serum glucose mildly elevated at 120 mg/dL. All serum electrolytes are normal: sodium, 140 mEq/L; potassium, 4 mEq/L; chloride, 98 mEq/L; carbon dioxide, 25 mEq/L; and magnesium, 1.5 mEq/L. Stephen F.’s blood alcohol concentration on admission is 150 mg/dL (normal: 0 mg/dL). His serum GGT is 321 International Units/L, and his AST is 87 International Units/L.
Unfortunately, efforts at treating hepatic encephalopathy do not reverse his coma. Further examination and testing are undertaken when it is noted that his ammonia concentration is normal at 48 mcg/dL. Then, a large bruise is noticed on the side of Stephen F.’s head, and a CT scan reveals a large subdural hematoma. With surgical treatment of the hematoma, he promptly awakes and asks for more beer.
QUESTION: How does one establish the diagnosis of hepatic encephalopathy for this patient? What is the role of the serum ammonia concentration in the diagnosis?
DISCUSSION: This case demonstrates that the diagnosis of hepatic encephalopathy is not always straightforward. Hepatic encephalopathy is only one cause of altered mental function in patients with advanced liver disease. Other causes may include accumulation of drugs with CNS depressant properties, head trauma, hypoglycemia, delirium tremens, and electrolyte imbalances. The diagnosis of hepatic encephalopathy is suggested by the following:
Elevated ammonia concentrations
Presence (in early stages) of asterixis or a flapping tremor of the hands
The response to therapy (usually correction of electrolyte imbalances, rehydration, and lactulose and/or rifaximin) further supports this diagnosis. Serum ammonia concentrations, therefore, are just one piece of this puzzle. An elevated concentration suggests, but does not establish, this diagnosis. Furthermore, although normal ammonia concentrations may cause one to question the diagnosis of hepatic encephalopathy, they can occur in this condition.
Laboratory Diagnosis of Acute Hepatitis
Michael C., a 45-year-old executive, presents to his physician after noticing that he has been turning yellow. Other than increased fatigue, he says he feels well. His physical examination is normal except for his jaundice and tenderness over a slightly swollen liver. Initial laboratory studies show elevations of the aminotransferases, with an ALT of 1,235 International Units/L and an AST of 2,345 International Units/L. His total bilirubin is 18.6 mg/dL.
The tentative diagnosis is acute hepatitis. However, Michael C. has not had any transfusions, used parenteral drugs, or had recent dental work. No exposure to medications or occupational exposure accounts for the disease, and there is no family history of liver disease. Careful review of his history offers no explanation for his development of hepatitis.
Ultimately, serologies show a positive HBsAg and anti-HBc antibody. A diagnosis of acute type B hepatitis is established. After much questioning, Michael C. reveals that he had a “brief encounter” with a prostitute on a recent business trip. His wife is treated with the vaccine and hepatitis B immunoglobulin, a γ-globulin with high concentrations of antibodies to HBsAg, and she does not develop hepatitis.
QUESTION: How is this diagnosis established? How should Michael C. be followed, and what is the likely outcome?
DISCUSSION: This case demonstrates why a determination of the etiology of hepatitis is often difficult. The practitioner must obtain a detailed history of exposures to medicines, drugs, alcohol, infected people, family members with similar illness, and ongoing medical illness. In this case, the exposure to the prostitute put Michael C. at risk for hepatitis B, C, and D and for HIV. The diagnosis is established by the serologies. If just the anti-HBc antibody had been present, he could have
been in the “window” of the acute phase of the disease where this antibody is positive and HBsAg is negative
previously recovered from hepatitis B
been a chronic carrier
Although the additional presence of HBsAg helps to secure the diagnosis, the clinical picture must be considered. Both HBsAg and anti-HBc also can be positive in patients with chronic hepatitis B. Determination of the type of hepatitis has prognostic value and, in this case, allows administration of prophylactic medications to people who might have been exposed.
Acute infection or chronic hepatitis B
Resolving hepatitis B or previous infection
Resolving or recovered hepatitis B or patient after vaccination
There is no generally accepted drug therapy for type B acute viral hepatitis. Michael C. should have repeated physical examinations and repeat laboratory testing for albumin, INR, AST, ALT, and bilirubin. There is a >1% chance that he will develop fulminant hepatitis and die. Most likely, he will recover completely, with his LFTs normalizing over 1 to 2 months. However, there is a 10% to 20% chance that he will develop chronic hepatitis, which could lead to cirrhosis.
Laboratory Diagnosis of Hepatitis Type C
Katherine M., a 48-year-old woman, receives a notice 2 weeks after donating blood that it could not be used because her aminotransferases are elevated and a test for hepatitis C is positive. She is referred to a specialist; her ALT is 87 International Units/L, her AST is 103 International Units/L, and her bilirubin is 0.8 mg/dL.
A liver biopsy demonstrates chronic active hepatitis. After considerable discussion, Katherine M. is placed on oral drug therapy for hepatitis C. After 3 months of therapy, however, her aminotransferases are not responding, and she is referred for a second opinion.
Viral hepatitis C infection is excluded when her laboratory results are repeated, and she is found to have negative titers to detect HCV RNA (PCR). Additional history is then obtained. Katherine M. reluctantly tells her local family physician that about 6 months previously, she had a positive skin test for tuberculosis (TB) after discovering that her partner is HIV positive. She also says she sought treatment in a nearby city, had been placed on isoniazid, and finished the prescription but never returned to the clinic.
QUESTION: What are the roles of the second-generation and third-generation tests in the diagnosis of hepatitis C? What other nonviral forms of hepatitis can present as chronic hepatitis?
DISCUSSION: This case demonstrates several points. Many patients with chronic active hepatitis remain totally asymptomatic—their disease first being detected during routine blood work or when symptoms of cirrhosis or liver failure develop. Now that all blood donors are checked for hepatitis C and abnormal aminotransferases, many patients with chronic liver disease are detected before symptoms are present. Unfortunately, however, blood banks tend to use the less expensive and less accurate ELISA testing for hepatitis C, which (as in this case) gives many false-positive results. Before starting therapy or establishing a diagnosis of type C hepatitis, a practitioner should confirm the diagnosis with RT-PCR.
A similar picture also may be seen in autoimmune hepatitis, Wilson disease, α1-antitrypsin deficiency, and hemochromatosis. Isoniazid, a common medication for TB, can cause serious liver damage that may be clinically and histologically indistinguishable from viral chronic active hepatitis. Therefore, aminotransferases need to be carefully monitored in patients on this drug. This problem tends to occur in patients over the age of 50, particularly women.
The aminotransferases may only be minimally elevated, as in this patient. Generally, hepatitis develops after about 2 to 3 months of drug therapy. With withdrawal of the medication, the numbers usually return to normal over an additional 1 to 2 months. When the diagnosis of chronic active hepatitis is considered, a patient’s medications must be carefully reviewed.
A Case of Acute Liver Failure
Matthew Z., an 18-year-old high school senior, notices he is becoming increasingly tired and somewhat weak. He initially is taken to a local clinic where he is reassured that most likely he is getting the “flu” and is sent home. Over the next day, he becomes progressively weaker, and his family notices that he is becoming yellow. He is taken to his physician.
He denies being on any medications or supplements. There is no family history of liver disease. Matthew Z. denies alcohol use. There has been no recent history of unusual travel.
Initial physical examination is unremarkable except for his being markedly icteric (jaundiced) and his liver being somewhat enlarged.
Laboratory findings include ALT 1,354 International Units/L, AST 1,457 International Units/L, and total bilirubin 12.5 mg/dL. Serum ALP is 245 International Units/L.
The tentative diagnosis is acute viral hepatitis. However, as more laboratory results come back, this diagnosis is increasingly under question because they show negative serologies for hepatitis A, B, C, and E. Evaluation for autoimmune hepatitis is negative as well with a negative antinuclear antibody (ANA) and antismooth muscle antibody. Serologies for mononucleosis and cytomegalovirus are negative as well.
Matthew Z. is admitted to the hospital; over the next 2 days, his total bilirubin progressively climbs to 23.4 mg/dL and his INR increases to 4. He becomes increasingly confused and lethargic, and a serum ammonia level is found to be elevated at 348 mcg/dL.
A diagnosis of acute liver failure is made, and he is transferred to a liver transplant center where he admits that in the days before the onset of his illness, he had visited his girlfriend in college and they both took some ecstasy (MDMA, 3,4-methylenedioxy-N-methylamphetamine).
QUESTION: What is acute liver failure and what generally causes it?
DISCUSSION: Acute liver failure refers to the rapid development (typically within 8 weeks) of severe liver injury with associated failure of the liver to perform its usual synthetic/detoxifying functions. In this case, it is evident by the elevated bilirubin, prolonged INR, and the development of hepatic encephalopathy. There are many potential causes, such as drug or toxin related, with acetaminophen being among the most common culprits. Viral hepatitis can cause this picture, as can ischemia of the liver, sepsis, autoimmune hepatitis, malignancy, and certain conditions associated with pregnancy.
MDMA hepatotoxicity is increasingly common in young people, as this drug is increasingly used. It can cause subclinical liver damage, including fibrosis, and is rarely associated with a picture of fulminant liver failure as in Matthew Z. Treatment is largely supportive and may involve liver transplantation.
A Case of Drug-Induced Hepatotoxicity
Darcie D. is a 43-year-old executive who presents to her doctor because she is not feeling well. She has become increasingly fatigued, lost her appetite, and just feels “sick.”
Her past medical history is generally unremarkable; she does not smoke, drinks only socially, and does not take any medications or supplements. Physical examination is entirely normal.
Screening laboratory tests include a normal complete blood count (CBC), BUN, serum creatinine, and serum electrolytes. LFT results, however, are remarkable: ALT 257 International Units/L and AST 397 International Units/L. Her bilirubin is elevated at 2.3 mg/dL, and alkaline phosphatase is elevated at 367 units/L.
Additional laboratory findings include negative serologies for hepatitis A, B, and C. Tests to rule out autoimmune hepatitis (ANA, AMA) are negative, and tests to exclude hemochromatosis (iron, TIBC, and ferritin) are also normal.
Darcie D. presents again to her doctor’s office, and on further questioning, she says that 3 weeks before, while on a business trip to California, she developed a bad cold and had been given azithromycin “Z-pak” at a local clinic. Over the next 2 weeks, Darcie’s D.’s laboratory results gradually return to normal, and she reports feeling better.
QUESTION: Is it common for patients to develop symptomatic hepatitis weeks to months after exposure to hepatotoxins?
DISCUSSION: When we think of hepatotoxic agents (drugs, supplements, toxins), we tend to limit our thinking to a patient’s current exposures. Usually, this alone solves our diagnostic dilemma. It is useful, however, to realize that often hepatoxicity can present weeks (occasionally months) after exposure. One classic agent that can present this way is amoxicillin–clavulanate. Azithromycin can present with jaundice, abdominal pain, pruritus, and evidence of hepatocellular injury weeks after a brief exposure. Treatment is generally supportive.
A Case of Nonalcoholic Steatohepatitis
Allen K., a 48-year-old corporate executive, presents for his required company physical examination. He had no medical complaints, has a negative past medical history, and is not taking any medications. He denies alcohol use.
Physical exam reveals weight 240 lb and height 5′10″. His blood pressure is elevated at 154/98. The rest of his physical examination is normal.
Laboratory data include a normal CBC and kidney function, fasting glucose 129 mg/dL, and elevated cholesterol. His LFT results are elevated with ALT 134 International Units/L and AST 105 International Units/L. His serum bilirubin, albumin, ALP, and INR are all normal.
He is referred for evaluation of his abnormal liver panel, and further testing shows no evidence of viral hepatitis, hemochromatosis, or autoimmune liver disease. The possibility of fatty liver is raised, and a liver biopsy is performed, which shows NASH with early cirrhosis.
QUESTION: What is NASH, and how is it treated?
DISCUSSION: Our society is experiencing a marked increase in the incidence of obesity. Many of these patients develop what is defined as metabolic syndrome, which must have three of the following factors: abdominal obesity, elevated blood pressure, impaired glucose tolerance, or hyperlipidemia. Obese patients, particularly those with the metabolic syndrome, are at a higher risk of developing nonalcoholic fatty liver disease or fatty liver. Some patients with fatty liver can progress to NASH and ultimately to cirrhosis and liver failure. Progression to NASH is usually associated with abnormal LFTs. As in this case most patients who progress to cirrhosis have no symptoms to suggest progressive liver disease at the time the diagnosis is ultimately made. Although many drugs have been tried in these cases, ultimately the only accepted treatment is weight loss through diet and occasionally surgery, including laparoscopic gastric bypass, gastric sleeves, or banding. Fatty liver also can be caused by rapid weight loss, parenteral nutrition, medications (such as steroids, estrogens, amiodarone), and short bowel syndrome.
Chronic pancreatitis, generally due to chronic inflammation of the pancreas leading to progressive fibrosis and calcification, can lead to the development of diabetes mellitus or malabsorption caused by deficiencies in the production of pancreatic hormones (insulin) or enzymes.
Gallstones and alcohol abuse are causative factors in 60% to 80% of acute pancreatitis cases. Medications can also cause acute pancreatitis (Table 15-8). Other possible causes include trauma (a typical example being an injury due to a bicycle handlebar), penetrating ulcers, hypercalcemia, hypertriglyceridemia, pancreatic neoplasm, and hereditary or autoimmune pancreatitis. Often, however, it is impossible to determine the definite cause of a patient’s attack. The tests discussed in this section, amylase and lipase, are primarily used to diagnose pancreatitis, although they may be clinically useful in the diagnosis of other pathologies. Of note is that lipase is increasingly the test of choice in the diagnosis of pancreatitis.
aA good review on drug induced pancreatitis, with a much more inclusive list is seen in Jones MR, Hall OM, Kaye AM, et al. Drug induced pancreatitis: A review. Ochsner J; 2015 (Spring); 15:45–51.
Normal range: 20 to 96 units/L (method dependent) (0.34 to 1.6 µkat/L)
Amylase is an enzyme that helps break starch into its individual sugar molecules. The most frequent clinical use of measuring serum amylase levels is in the diagnosis of acute and chronic pancreatitis. Although amylase levels have long been used for this diagnosis, increasingly lipase (see later discussion) is preferred in part due to its longer half-life and greater specificity.
As with any serum protein, concentrations result from the balance between entry into circulation and rate of clearance. Most circulating amylase originates from the pancreas and salivary glands. These sources are responsible for approximately 40% and 60% of serum amylase, respectively. However, the enzyme is also found in the lungs, liver, fallopian tubes, ovary, testis, small intestine, skeletal muscle, adipose tissue, thyroid, tonsils, and certain cancers, and various pathologies may increase secretion from these sources. The kidneys are responsible for about 25% of the metabolic clearance, with the remaining extrarenal mechanisms being poorly understood. The serum half-life is between 1 and 2 hours. Patients with azotemia can have decreased amylase clearance and elevated amylase levels. More than half of the patients who have a low creatinine clearance between 13 and 39 mL/min have elevated amylase levels. Although there is no amylase activity in neonates and only small amounts at 2 to 3 months of age, concentrations increase to the normal adult range by 1 year of age.
Amylase concentrations rise within 2 to 6 hours after the onset of acute pancreatitis and peak after 12 to 30 hours if the underlying inflammation has not recurred. In uncomplicated disease, these concentrations frequently return to normal within 3 to 5 days. More prolonged, mild elevations occur in up to 10% of patients with pancreatitis and may indicate ongoing pancreatic inflammation or associated complications (eg, pancreatic pseudocyst).
Although serum amylase concentrations do not correlate with disease severity or prognosis, a higher amylase may indicate a greater likelihood that the patient has pancreatitis. For example, serum amylase concentrations may increase up to 25 times the upper limit of normal in acute pancreatitis, while elevations from opiate-induced spasms of the sphincter of Oddi generally are <2 to 10 times the upper limit of normal. Unfortunately, the magnitude of enzyme elevation can overlap in these situations, and ranges are not very specific. Most guidelines require a 3-fold elevation in amylase (or lipase) as one of the criteria for establishing this diagnosis. The other two criteria are characteristic symptoms and an abnormal imaging study. Two criteria are generally required.
Amylase has a relatively low sensitivity, with about 20% of patients with acute pancreatitis having normal levels. This is especially common in patients with alcoholic pancreatitis or pancreatitis due to hypertriglyceridemia. Additionally, amylase has relatively low specificity and may be elevated in a wide range of conditions. These include a variety of diseases of the pancreas, salivary glands, GI tract (including hepatobiliary injury, perforated peptic ulcer, and intestinal obstruction or infarction), and gynecologic system (eg, ovarian or fallopian cysts) as well as pregnancy, trauma, renal failure, various neoplasms, and diabetic ketoacidosis. Additionally, alcohol and a variety of medications including, but not limited to, aspirin, cholinergics, thiazide diuretics, and oral contraceptives may also cause increased values.34 In diagnosing acute pancreatitis, other useful laboratory tests include lipase because it is confounded by fewer factors and fractionation of serum amylase into pancreatic and salivary isoenzymes (although its use has been questioned).
Another condition that may cause elevated amylase concentrations is macroamylasemia, a benign condition present in 2% to 5% of patients with hyperamylasemia. In this condition, amylase molecules are bound by immunoglobulins or complex polysaccharides, forming aggregates that are too large to enter the glomerular filtrate and be cleared by the kidneys. This results in serum concentrations up to 10 times the normal limit. Macroamylasemia can be detected by fractionating serum amylase or by measuring urine amylase.
Urine amylase concentrations (normal range: <32 International Units for a 2-hour collection or <384 International Units for a 24-hour collection) usually peak later than serum concentrations, and elevations may persist for 7 to 10 days. This is useful if a patient is hospitalized after acute symptoms have subsided at which point serum amylase may already have returned to normal, leaving only urinary amylase to indicate pancreatitis. As discussed next, lipase may also persist after serum amylase levels decline. Urine amylase levels may also be useful in revealing macroamylasemia, in which case serum amylase is elevated, while urinary amylase is normal or decreased. However, this pattern of elevated serum amylase without elevated urinary amylase is also consistent with renal failure.
One cause of amylase’s relatively low sensitivity is that marked hypertriglyceridemia may cause amylase measurements to be artificially low, masking an elevation in serum amylase. This finding is clinically relevant because hypertriglyceridemia (>800 mg/dL) is a potential cause of acute pancreatitis. In this situation, serial dilution of the serum specimen can eliminate the assay interference of hypertriglyceridemia, and elevated amylase values can be identified and measured. Fortunately, urinary amylase and serum lipase would typically be abnormal in this situation, which is another way to assess patients suspected of having elevated serum amylase levels.
Normal range: 3 to 43 units/L (0.51 to 0.73 µkat/L)
Lipase is an enzyme secreted by the pancreas that is transported from the pancreatic duct into the duodenum where it aids in fat digestion. Lipase catalyzes the hydrolysis of triglycerides into fatty acids and a monoglyceride that are more readily absorbed by the small intestine. Although mostly secreted by the pancreas, lipase can also be found in the tongue, esophagus, stomach, small intestine, leukocytes, adipose tissue, lung, breast milk, and liver. In healthy individuals, serum lipase tends to be mostly of pancreatic origin.
Lipase initially parallels amylase levels in acute pancreatitis, increasing rapidly and peaking at 12 to 30 hours. However, lipase has a half-life of 7 to 14 hours so that it declines much more slowly, typically returning to normal after 8 to 14 days. Thus, one utility of lipase (similar to urinary amylase) is the detection of acute pancreatitis roughly ≥3 days after onset, at which point amylase levels may no longer be elevated. As with amylase, peak lipase concentrations typically range from three to five times the upper limit of the reference range.
A comparison of the sensitivity and specificity of amylase versus lipase, and the use of these tests alone or in combination, is debated. This issue is complicated by the fact that the sensitivity and specificity of any laboratory test varies depending on where the cutoff is chosen (eg, choosing a higher cutoff increases specificity at the cost of lower sensitivity). In general, serum lipase appears to be superior, particularly with respect to specificity. However, simultaneous determination of both lipase and amylase may increase overall specificity because different factors confound the different assays. For example, an elevated amylase with a normal lipase suggests amylase of salivary origin or may represent macroamylasemia. Similarly, an elevated lipase with normal amylase has often been shown not to be due to pancreatitis, although in the case of pancreatitis it could be caused by delayed laboratory evaluation or artificial lowering of amylase levels by hypertriglyceridemia.35
Lipase concentrations may be elevated in patients with nonpancreatic abdominal pain, such as a ruptured abdominal aortic aneurysm, and a variety of disorders of the alimentary tract and liver, such as intestinal infarction. This is because lipase is located in these organs. Renal failure, nephrolithiasis, diabetic ketoacidosis, and alcoholism are conditions in which lipase elevations tend to be present but usually in concentrations less than three times the upper limit of the reference range. Drug-induced elevations in lipase can be attributed to opioids (codeine, morphine), nonsteroidal antiinflammatory drugs (NSAIDs; indomethacin), and cholinergics (methacholine and bethanechol). In the condition of macrolipasemia, similar to macroamylasemia but far less frequent, macromolecular complexes of lipase to immunoglobulin prevent excretion and elevate serum lipase concentrations.36
Other Test Results in Pancreatitis
In severe cases of acute pancreatitis, occasionally several days after the insult, fat necrosis may result in the formation of organic soaps that bind calcium. Serum calcium concentrations then decrease (low albumin may also contribute), sometimes enough to cause tetany. When pancreatitis is of biliary tract origin, typical elevations in ALP, bilirubin, AST, and ALT are seen. Some researchers believe that in acute pancreatitis an increase of ALT to three times baseline or higher is relatively specific for gallstone-induced pancreatitis.
Pancreatitis also may be associated with hemoconcentration and subsequent elevations of the BUN or hematocrit. Depending on the severity of the attack, lactic acidosis, azotemia, anemia, hyperglycemia, hypoalbuminemia, or hypoxemia may also occur.
Despite the performance of amylase and lipase assays for acute pancreatitis, the sensitivity and specificity of these tests are often regarded as unsatisfactory, and in some patients, pancreatitis is only diagnosed on autopsy. For this reason, several new tests have been investigated (eg, serum trypsin and trypsinogen), although they are not yet widely available. Ultimately, it is recognized that the lack of sensitivity for both amylase and lipase implies that these tests can be used to support a diagnosis of acute pancreatitis but may not definitively provide a secure diagnosis, particularly if the levels are not dramatically elevated. Recent practice guidelines suggest that two of the following are needed to diagnose acute pancreatitis: (1) characteristic symptoms; (2) elevation of amylase or lipase to at least three times normal; (3) characteristic findings on imaging (usually CT or MRI) (Minicase 12, Minicase 13).
James T., a 55-year-old man, develops a vague but persistent epigastric pain that radiates to his back. He notes that his appetite is “off,” and his clothes are getting much looser on him. His pain is not related to eating, activity, or position.
He presents to his primary care physician, who documents that he lost about 25 lb in the past year. His physical examination is unremarkable. Laboratory data show a normal CBC, renal function, and LFTs. His amylase and lipase are both elevated, with a serum amylase of 189 units/L and a lipase of 390 units/L. Serum calcium and triglycerides are normal.
There are no identifiable precipitating causes noted. The first consideration is that he might have acute or even chronic pancreatitis.
A CT scan shows a pancreatic mass. He is referred to a surgeon for consideration of surgery, with a presumptive diagnosis of pancreatic carcinoma. James T. and his family, however, get a second opinion. Further workup shows an elevated ANA and a serum IgG4 markedly elevated at 464 mg/dL (normal being up to 140 mg/mL).
The diagnosis of autoimmune pancreatitis is suggested, and James T. is offered a pancreatic biopsy. He elects for a 2-week trial of steroids. Prednisone is started at 40 mg/day. Two weeks later, he reports feeling better, and his CT demonstrates a marked reduction in the size of his mass.
QUESTION: How do we diagnose autoimmune pancreatitis?
DISCUSSION: Autoimmune pancreatitis is a new recognized disease in which patients can present with findings often indistinguishable from pancreatic cancer or chronic pancreatitis. The diagnosis is suggested if other autoimmune diseases are present, including Sjögren syndrome, autoimmune thyroid diseases, and autoimmune renal diseases. In this patient, the presence of a markedly elevated IgG4 level is highly suggestive of this autoimmune disease. The biopsy would likely have been diagnostic. However, a rapid response to steroids is virtually diagnostic of this condition. In some cases, the steroids can be tapered down, and some patients require ongoing immunosuppressive therapy, usually with azathioprine.
The importance of making this diagnosis is in providing appropriate therapy and avoiding what would have been extensive, life-changing surgery. The patient’s steroids were tapered over a period of time, and his CT results did revert to normal.
Abdominal Pain in a Young Woman
Betsy L., a 32-year-old woman, presents with a sudden onset of severe epigastric pain radiating to her back. She has tried antacids without any relief. This began after a night of heavy partying and drinking. Her past history is otherwise unremarkable. She and her family deny a history of chronic alcohol abuse. Physical examination shows some tenderness in her epigastric area, which is otherwise benign. Lab studies showed a normal CBC, and her lipase is markedly elevated at 1,382 units/L, with an elevated ALT of 592 units/L and an AST of 649 units/L. Her total bilirubin is elevated at 2.8 mg/dL. Serum lipid profile and calcium are normal. She is admitted to the hospital with a diagnosis of alcohol-induced pancreatitis.
QUESTION: Does she really have alcoholic pancreatitis? What else might be going on here?
DISCUSSION: Typically, alcoholic pancreatitis does not occur just after an occasional episode of binge drinking; it is generally seen in people with a long history of chronic alcohol abuse. Her LFT results are markedly abnormal, suggesting a hepatobiliary etiology. Additionally, serum lipase levels >1,000 do not suggest alcoholic-induced pancreatitis but suggest a surgical cause of her pancreatitis. In this case there were no medications that could have caused her attack and no history of abdominal trauma. Her lipids and calcium were normal.
An ultrasound of her abdomen showed gallstones in a somewhat inflamed gall bladder, dilated biliary ducts, and a 1-cm stone in her distal bile duct. An endoscopic retrograde cholangiopancreatography was undertaken with removal of the stone, and subsequently she underwent a laparoscopic cholecystectomy.
Gallstone disease is one of the two most common causes of acute pancreatitis in the United States, the other being alcohol. The mechanism, while not completely understood, seems to be the passing of a stone from the gallbladder, down the common bile duct, and through the ampulla. In the ampulla, it may serve to block the pancreatic duct, and indeed sometimes a stone will lodge at that site. Additionally, it may cause reflux of bile into the pancreatic duct. In most cases, by the time of diagnosis, the offending stone has passed, and the approach would be to remove the gallbladder (preferably during the same hospitalization) to prevent recurrent attacks. In this case, the stone had not passed, and it was removed endoscopically prior to the surgery.
Up to 10% of the U.S. population develops duodenal or gastric ulcers at some point in life. Previously, ulcers were believed to be primarily due to acid. Traditional therapy with antacids, histamine-2-antagonists, and proton pump inhibitors (PPIs) have been effective in treating ulcers, but they are not as effective in preventing recurrences, in part because they do not eradicate the underlying bacterial cause.
H pylori has been identified as a cause of ulcer disease, and studies into its detection and treatment are still in a state of rapid development.37H pylori is a gram-negative bacillus, usually acquired during childhood, that establishes lifelong colonization of the gastric epithelium in affected individuals. Transmission seems to be by the fecal–oral or oral–oral route. Prevalence increases with age and correlates with poor sanitation. By the age of 50, 40% to 50% of people in developed countries and >90% of people in developing countries harbor these bacteria.38
H pylori infection may be found in >90% of patients with duodenal ulcers and >80% of patients with gastric ulcers. Furthermore, the bacterium has been associated with the development of gastritis, gastric cancer, and certain types of gastric lymphoma. The most common lymphoma associated with H pylori is mucosa-associated lymphoid tissue, which is often curable just by treating the underlying H pylori infection. However, most infected individuals (>70%) are asymptomatic, and eradication therapy remains a controversial subject for asymptomatic colonization. From the other perspective, H pylori-infected individuals have a 10% to 20% chance of developing peptic ulcers and a 1% to 2% chance of developing gastric cancer during their lifetime. Candidates for screening for H pylori include those with active ulcer disease, history of ulcer disease, and certain gastric lymphomas. Screening should be considered prior to long-term therapy with aspirin or NSAIDs or in patients under the age of 60 with chronic dyspepsia. One problem in managing patients with H pylori infection is that treatment is not always successful in eradicating this bacterium, in part due to increasing resistance to antibiotics. In the United States, rates of resistance to metronidazole (20% to 40%) and clarithromycin (10% to 15%) have been documented.
Helicobacter pylori-Associated Gastric Cancer
H pylori-associated gastric cancers account for about 5.5% of all cancers worldwide and about one-fourth of all infection-associated cancers. Its colonization is a key component for the development of gastric cancer; however, other factors, such as atrophic changes in the stomach, are needed for this to occur. Atrophic gastritis, characterized by chronic inflammation of the gastric mucosa, decreases and ultimately inhibits the ability of the stomach to secrete acid. Eradication of H pylori infection before atrophic changes occur can provide protection from gastric cancer. Individuals who have already suffered irreversible atrophic changes may still receive some benefit but should be considered at risk even after eradication. Currently, there is no effective H pylori vaccine available, so bacterial eradication must be executed with antibiotic therapy.
The diagnostic tests for H pylori are classified as noninvasive (serology, urea breath test, and fecal antigen test) or invasive (histology, culture, and rapid urea test)—the latter depending on upper endoscopy and biopsy. The serological test for H pylori detects circulating IgG antibodies against bacterial proteins. It has a relatively low sensitivity and specificity (80% to 95%) but has advantages of being widely available and inexpensive. Although useful to establish an initial diagnosis of H pylori, it should not be used to monitor the success of eradication therapy because antibody titers decrease slowly in the absence of bacteria.
The urea breath test is based on the ability of the bacteria to produce urease, an enzyme that breaks down urea and releases ammonia and carbon dioxide as its products. In the breath test, 13C- or 14C-labeled urea is given by mouth. If the bacteria are present, the radiolabeled urea is metabolized to radiolabeled CO2, which may be measured in exhaled air. The tests have high sensitivity and specificity (both 90% to 95% for 13C and 86% to 95% for 14C). However, the 14C isotope has the drawback of being radioactive, and the 13C isotope requires the use of sophisticated detection methods such as isotope ratio mass spectrometry (although samples are stable and may be sent off for analysis).
The fecal antigen test detects H pylori proteins in stool via ELISA. It has high sensitivity and specificity, both 90% to 95%. Like the urea breath test, the fecal antigen test is a very accurate noninvasive measure that is used primarily to monitor the success of eradication therapy. The fecal antigen test may not be appropriate for patients with active GI bleeding because of a cross-reactivity with blood constituents in the immunoassay, which can produce a high incidence of false-positive results. Patients undergoing urea breath tests or fecal antigen tests need to discontinue PPIs for 2 weeks before these tests are conducted because PPIs may decrease the numbers of H pylori in the stomach and decrease test accuracy.
Upper endoscopy with biopsy of gastric tissue and subsequent histologic examination has high sensitivity and specificity (88% to 95% and 90% to 95%, respectively) with the added advantage of allowing detection of gastritis, intestinal metaplasia, or other histologic features. Although not commonly performed, biopsy specimens may also be used to culture H pylori. By performing various tests on the cultured bacteria, this test may be rendered highly specific (95% to 98%), but the bacterium is difficult to culture, making this the least sensitive test (80% to 90%). The main advantage of culture is that it allows for antibiotic sensitivity testing, which can help optimize therapy and possibly prevent treatment failure. A rapid urease test (also known as the Campylobacter-like organism test) involves incubating a biopsy specimen in the presence of urea and a pH indicator. As mentioned previously, H pylori metabolizes urea, releasing ammonia, which in this case may be detected by its effect of increasing the pH. This test allows for rapid results (eg, 1-hour incubation time following endoscopy), high sensitivity and specificity (both 90% to 95%, respectively), and low cost. One proposed strategy is to take several biopsies at the time of endoscopy and first check the rapid urease test, sending specimens for detailed pathologic analysis only if the urease test is negative (or tissue diagnosis is needed to sort out other diagnoses).
All of these tests, with the exception of serology, tend to be confounded by factors that lower bacterial burden. In patients with achlorhydria or patients being treated with antisecretory drugs (eg, PPIs), increased stomach pH decreases bacterial levels and may lead to false-negative results. Similarly, use of bismuth or antibiotics (including recent, unsuccessful eradication therapy) may decrease test sensitivity. Recommendations advise waiting 2 to 3 months after finishing therapy before performing these tests to determine whether H pylori has been successfully eradicated and additionally holding PPIs for 2 weeks.
Although GI bleeding may confound the rapid urease test and the fecal antigen test, urea breath tests remain a viable diagnostic option in patients with active bleeding, detecting 86% of H pylori-positive patients.
Colitis—acute or chronic inflammation of the colon—often presents quite dramatically with profound and bloody diarrhea, urgency, and abdominal cramping. It is generally distinguished from noninflammatory causes of diarrhea on the basis of physical signs, including fever, abdominal tenderness, and an elevated white blood cell (WBC) count in the blood.
There are many causes of colitis. Infectious colitis may be caused by invasive organisms, including Campylobacter jejuni, Shigella, Salmonella, and invasive Escherichia coli. Amoeba can present in this manner, as can certain infections associated with HIV/AIDS; for example, cytomegalovirus and herpes virus have also been found to cause a colitis picture. Recently COVID-19 has been found to be associated with diarrheal symptoms, including a colitis picture.39 Noninfectious colitis includes ischemic colitis, drug-induced colitis (as with gold salts or NSAIDs), inflammatory bowel disease (Crohn’s disease or ulcerative colitis), and radiation injury. C difficile colitis, which is discussed in the next section, is a relatively new disease that has emerged as a major cause of hospital-acquired infection over the past 40 years, largely caused by the widespread use of broad-spectrum antibiotics.
C difficile colitis is a toxin-induced bacterial disease, which has become increasingly common and progressively more difficult to treat. Most infections follow antibiotic use, which reduces the normal bacterial flora of the colon and produces a niche for supra-infection by C difficile.40 As such, C difficile infection only became common following widespread use of broad-spectrum antibiotics in the 1960s. C difficile infection is most commonly associated with, but not limited to, exposure to fluoroquinolones, clindamycin, cephalosporins, and β-lactamase inhibitors. Clinical symptoms of infection range from an asymptomatic carrier state to chronic diarrhea, acute colitis, and life-threatening colitis with sepsis. Attacks can occur weeks after antibiotic therapy. Severe C difficile colitis is marked by a characteristic appearance of pseudomembranes, which consist of inflammatory exudates or yellowish plaques on the colonic mucosa and is thus referred to as pseudomembranous colitis. Milder cases present with inflammation limited to the superficial colonic epithelium; however, in severe cases there can be necrosis of the full thickness of the colonic wall.41
Clostridia species have the ability to form spores that can survive extreme environmental conditions and remain viable for years. Spores tend to persist within the hospital environment where they may infect patients receiving antibiotics, causing C difficile to be the most common cause of infectious diarrhea in hospitalized patients.
C difficile produces clinical disease by secreting various toxins within the colon. Toxins A and B are the most common toxins produced, with >90% of pathogenic strains producing toxin A. These toxins affect the permeability of enterocytes, trigger apoptosis, and stimulate inflammation. Some emerging strains also produce a binary toxin, which is associated with a more severe illness. The bacterium itself is not pathogenic, and some strains of C difficile do not produce toxins and are therefore harmless.
About 3% of healthy adults and 20% of hospitalized patients are asymptomatically colonized with C difficile bacteria. Unlike other similar hospital-infections (eg, Staphylococcus aureus), asymptomatic carriage of C difficile bacteria actually reduces the likelihood of developing clinical disease, even after antibiotic exposure. This is probably because people who are asymptomatically colonized have developed antibodies that neutralize the C difficile toxins or have harmless strains of C difficile, which produce no toxin (yet occupy a niche in the colon preventing infection by toxigenic strains).
Recently, several outbreaks have resulted from a new strain of C difficile bacteria that is resistant to fluoroquinolones (eg, ciprofloxacin, moxifloxacin).42 This strain expresses a binary toxin (until now generally not seen in clinical isolates) and upregulates its expression of toxins A and B by about 20-fold. Clinically, this correlates with ominous increases in morbidity and mortality. The continued emergence of C difficile strains with resistance to commonly used antibiotics and increased expression of virulence factors suggests that this bacterium will continue to be a serious complication of antibiotic use until a toxin vaccine can be developed. Current treatment consists of metronidazole (oral or IV) or vancomycin (oral or rectal), depending on severity; however, 20% to 30% of patients who receive therapy will face recurrent C difficile infection. Fidaxomicin, a more recently U.S. Food and Drug Administration–approved narrow spectrum macrolide for C difficile infection, may serve as a beneficial alternative therapy.43 A newer approach to treatment of C difficile involves fecal transplantation, in which stool is “donated” by a healthy donor and instilled into the GI tract of the infected patient.
Prevention of C difficile infection is largely based on avoidance of antibiotic therapy, unless absolutely necessary, and careful handwashing in hospitals and other institutional settings (including in-home patient care). C difficile spores are somewhat resistant to alcohol-based hand disinfectants, so washing with soap and water is preferred.
The diagnosis of C difficile can be challenging. There are a variety of tests available that vary in sensitivity, specificity, cost, availability, and timeliness. One important consideration is that patients with pseudomembranous colitis may deteriorate rapidly, so making a prompt and accurate diagnosis is important. In situations that clearly point to a diagnosis of C difficile in an acutely ill patient, it may be reasonable to initiate treatment on an empirical basis before the test results are even available. Hospitals and labs seem to have their own specific algorithms in terms of testing for C difficile. Diagnosis may also be made during lower endoscopy on encountering the characteristic white or yellow pseudomembranes on the colonic wall.
Generally, the most commonly used initial tests for C difficile infection are the ELISA assays for toxin or C difficile antigen within the stool. These tests are available in various commercial kits and have the advantage of being rapid, producing results within hours, and relatively inexpensive. Tests detect toxin A or both toxins A and B and have high specificity (typically >95%) but variable sensitivity (60% to 95%). For this reason, a negative test may be followed by one to two repeat tests to increase the composite sensitivity to the 90% range and exclude infection with more certainty. Testing for both toxins has a diagnostic advantage over testing for toxin A because a minority of strains are toxin A-negative and toxin B-positive. Alternatively, a negative test result is often confirmed with a PCR study (see later discussion).
Enzyme-linked immunosorbent assays for C difficile common antigen (glutamate dehydrogenase) have improved sensitivity but are less specific because they detect nontoxigenic species as well as some species of closely related anaerobes. Therefore, a positive assay for C difficile antigen does not prove pseudomembranous colitis and must be followed up with a toxin assay to prove the presence of a pathogenic C difficile strain. The advantage of this assay for C difficile antigen is that the sensitivity is better, such that a single negative assay may be used to exclude the presence of pseudomembranous colitis. The availability, performance, and appropriate use of these assays may vary among hospital laboratories, and inquiries should be made with the laboratory regarding which tests are available and the appropriate strategy for their use.
The “gold standard” test for pseudomembranous colitis has been the detection of toxin A or B in stool samples by demonstrating their cytopathic effect in cell cultures and inhibition of cytopathic effect by specific antiserum. Referred to as cell cytotoxicity assay, this test has excellent sensitivity (94% to 100%) and specificity (99%). However, these performance characteristics may be laboratory dependent. Moreover, this test is limited by high cost, a requirement for meticulously maintained tissue culture facilities, and a time delay of 1 to 3 days.
C difficile can also be cultured from stools with selective medium and identified with more traditional microbiologic techniques, including colony morphology, fluorescence, odor, gram stain, and signature gas liquid chromatography. Interestingly, this is not the most sensitive test for the organism. In addition, the bacterium is named difficile because of difficulty in culturing it. Another drawback is that isolated bacteria must then be tested for toxin production to avoid confusing it with nontoxic C difficile strains. Altogether, these factors make bacterial culture and toxin profiling a costly, time-consuming process; thus, they are rarely used. The primary advantage of this approach is that it isolates the organism, allowing genetic tests, which may aid in tracking mutant strains and determining the source of epidemics.
Nucleic acid amplification tests, including RT-PCR assays for the gene toxin A or B, not only provide fast and accurate diagnosis of C difficile but also provide the ability to identify if the pathogen is in the epidemic 027/NAP1/BI strain.44 This test is rapidly becoming a standard test for initial evaluation of C difficile infections. More typically it is being used if the initial test results (toxin, antigen studies) are negative. One issue with these tests is that they can detect asymptomatic carriers and should only be used in patients with frequent loose stools (Minicase 14).
Analysis of liver tests is complex and may be frustrating. Most tests in the LFT panel check for the presence of two broad categories of liver diseases—cholestasis versus hepatocellular injury. Therefore, an abnormal value may raise more questions than it answers. None of the tests is 100% sensitive or specific, and most may be confounded by a variety of factors. How, then, can these tests be used to answer clinical questions with any certainty?
Probably the most important point to bear in mind when interpreting LFTs is that they are but one piece of the puzzle. Correct interpretation relies on interpreting the test within the greater context of the patient, other laboratory data, historical information, and the physical exam.2,19 For example, mildly elevated bilirubin and ALP in the setting of a critically ill, septic patient is likely cholestasis of sepsis and does not necessarily require extensive evaluation. The same set of laboratory tests (mildly elevated bilirubin and ALP) in an ambulatory patient could be a sign of serious chronic illness such as PBC. However, if this same ambulatory patient had a history of normal LFTs and had recently started taking a medication known to cause cholestasis, then the abnormality would most likely be a side effect of the medication. Thus, the same set of liver tests in three different settings may have widely differing significance.
It is also important to interpret an abnormal value within the context of other laboratory tests, which is why LFTs are often obtained as a group (ie, the LFT panel). For example, a mildly elevated AST in the setting of an otherwise normal LFT panel might be of nonhepatic origin (eg, muscle disease). Alternatively, a mildly elevated AST combined with mildly elevated ALT might raise a concern about a mild hepatocellular process, perhaps chronic viral hepatitis or NASH. Finally, mildly elevated ALT and AST in combination with dramatically elevated ALP and bilirubin would point instead to a cholestatic process.
Antibiotic-Induced Pseudomembranous Colitis
Julia T., a 36-year-old woman, presents to her physician after several days of crampy abdominal pain, diarrhea, persistent fever up to 102.5°F, and chills. On physical examination, she is well hydrated. Her abdomen is soft and nontender. Stools are sent for pathogenic bacterial cultures, including Shigella, Salmonella, Campylobacter, entero-invasive E coli, and Yersinia; meanwhile, Julia T. is given a prescription for diphenoxylate.
Twenty-four hours later, Julia T. presents to the emergency department (ED) doubled over with severe abdominal pain. Her abdomen is distended and tender with diffuse rigidity and guarding. Clinically, she is dehydrated. Her WBC count is elevated at 23,000 cells/mm3 (3.54 to 9.06 × 103 cells/mm3), and her BUN is 34 mg/dL. Abdominal radiographs show a dilated colon (toxic megacolon) and an ileus. She then tells the ED physician that about 6 weeks earlier, she had taken two or three of her sister’s amoxicillin pills because she had thought she was developing a urinary tract infection. Although pseudomembranous colitis is tentatively diagnosed, Julia T. cannot take oral medication because of her ileus. Therefore, IV metronidazole and rectal vancomycin are started. She continues to get sicker, however, and early the next day, most of her colon is removed (the rectum was left intact), and an ileostomy is created.
QUESTION: What is the time course of pseudomembranous colitis? Did the use of diphenoxylate influence the outcome?
DISCUSSION: Pseudomembranous colitis can occur even after only one or two doses of a systemic antibiotic or after topical antibiotic use. Moreover, it can occur weeks after the last dose of antibiotic. A complete history of antibiotic use is critical when dealing with patients with diarrhea.
Diphenoxylate or loperamide use in the face of colitis is associated with an increased risk, although small, of toxic megacolon. In this medical emergency, the colon has no peristalsis. Together with the inflammation in the colon wall (colitis), toxic megacolon often leads to progressive distention. If untreated, perforation and death ensue. The development of a megacolon or ileus in this patient is especially worrisome because the best treatment—oral antibiotics—would be of little benefit. However, IV metronidazole is excreted into the bile in adequate bactericidal levels to eradicate the bacteria. Unfortunately, in the absence of peristalsis, its benefit would be questionable.
Therefore, liver tests should always be interpreted with a clear understanding of the clinical context and other laboratory abnormalities. Although the LFT panel rarely yields an exact diagnosis, it may indicate the type of process (eg, cholestatic versus hepatocellular) and the severity of the process (eg, fulminant liver failure versus mild hepatic inflammation), which leads the practitioner to a group of possibilities that may be further evaluated based on the information at hand, along with other laboratory tests or studies (eg, radiographs, endoscopic procedures, or tissue biopsies) as needed. The diagnostic yield of these tests also depends on their appropriateness and the thoughtfulness of their selection. Liver studies obtained to answer a specific clinical question (eg, “Does this patient have liver inflammation due to initiation of statin medications?”) are more likely to yield interpretable information than a less guided question (“Is this patient sick?”).
Some other aspects of gastroenterology and related laboratory tests are also reviewed in this chapter. Amylase and lipase may reflect pancreatic inflammation; H pylori may be related to ulcer disease; and C difficile is a major cause of hospital-acquired colitis. Although these tests are less convoluted than the LFT panel, it is still paramount to obtain them in a thoughtful manner and interpret the results in the appropriate clinical setting. For example, colonization with H pylori may be of little acute significance in an asymptomatic patient, whereas it may mandate an immediate course of multiple antibiotics in a patient with recurrent gastric ulcer bleeding.
1. Why is the term liver function test a misnomer?
ANSWER: Often, the term is used to describe a panel of tests, including AST, ALT, bilirubin, ALP, and albumin. However, the term is a misnomer because most of these tests do not measure liver function. The liver has several functions and different tests reflect these different functions. The following table divides liver tests into rough categories by function and type.
Synthetic liver function
Albumin, prealbumin, PT/INR
ALP, 5′ nucleotidase, GGT, bilirubin
2. What common disorders cause isolated increased indirect bilirubinemia versus direct bilirubinemia? Explain the pathophysiologic cause of the laboratory abnormality in each case.
ANSWER: Indirect bilirubin is produced by the breakdown of erythrocytes. Indirect bilirubin is delivered to the liver, where it is converted to direct bilirubin by glucuronyl transferase. Thus, an elevated level of indirect bilirubin may result from increased breakdown of red blood cells (hemolysis) or reduced hepatic conversion of indirect bilirubin to direct bilirubin. Common causes include hemolysis, Gilbert syndrome, and drugs, such as probenecid or rifampin.
Increased direct bilirubin usually implies hepatic disease, which interferes with secretion of bilirubin from the hepatocytes or clearance of bile from the liver. There are exceptions to this, Dubin-Johnson syndrome and Rotor syndrome being two benign abnormalities of bilirubin metabolism and excretion. Direct hyper-bilirubinemia, especially in the presence of other abnormalities in the LFT profile, is generally classified as reflecting hepatic cholestasis, although it may also be due to a hepatocellular process. In cholestatic disease, the bilirubin is primarily conjugated, whereas in hepatocellular processes, significant increases in both conjugated and unconjugated bilirubin may result. Cholestasis may be intrahepatic or extrahepatic. Intrahepatic cholestasis may be due to viral hepatitis, reactions to different medications, alcoholic hepatitis or cirrhosis, pregnancy, severe infection, or PBC. Extrahepatic cholestasis involves obstruction of the larger bile ducts either inside or outside of the liver, which can be due to strictures, stones, or tumors.
3. What is the relative importance of AST and ALT tests in terms of diagnosing hepatocellular disease?
ANSWER: Elevations of AST and ALT generally reflect inflammation in the liver. However, they are not associated with prognosis (higher levels do not suggest a worse prognosis) or with etiology. Although there is value in assessing the ratios of these two (for example an AST/ALT ratio of over two may suggest alcoholic liver disease), these tests do not “tell the whole story.” Evaluating a patient with suspected liver disease is a complex undertaking. The history must be obtained in detail, including present and past medications, supplements, vitamins, occupational exposure, underlying diseases, history of surgical procedures, history of transfusions, and drug use.
4. How is acute pancreatitis diagnosed?
ANSWER: The clinical presentation of acute pancreatitis generally consists of epigastric pain, often radiating to the back. There can be associated nausea, vomiting, diaphoresis, and fever. The challenge here is that these symptoms are not specific at all. Similar complaints can be seen with biliary disease, ulcers, gastritis, small bowel problems, or compromised blood supply to the gut. At times there can be overlap. Gallstones can migrate down the common bile duct, causing pancreatitis. Ulcers can penetrate the duodenum and invade the pancreas also causing pancreatitis. To establish a diagnosis of pancreatitis one looks for three things. First, the clinical picture should be consistent with this diagnosis. Second, a serum lipase or amylase should be over three times normal (realizing that these tests are not specific). Third, it is often of value (especially if the first two criteria are not both present) to have an advanced imaging study, either MRI or CT, showing pancreatitis. Generally, two of the three criteria should be present before diagnosing acute pancreatitis.
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