2555Evaluation of Liver Function CHAPTER 337

phosphatase and 5′-nucleotidase are found in or near the bile canalicular membrane of hepatocytes, whereas GGT is located in the

endoplasmic reticulum and in bile duct epithelial cells. Reflecting its

more diffuse localization in the liver, GGT elevation in serum is less

specific for cholestasis than are elevations of alkaline phosphatase or 5′-

nucleotidase. Some have advocated the use of GGT to identify patients

with occult alcohol use. Its lack of specificity makes its use in this setting questionable.

The normal serum alkaline phosphatase consists of many distinct

isoenzymes found in the liver, bone, placenta, and, less commonly, the

small intestine. Patients over age 60 can have a mildly elevated alkaline

phosphatase (1–1.5 times normal), whereas individuals with blood

types O and B can have an elevation of the serum alkaline phosphatase

after eating a fatty meal due to the influx of intestinal alkaline phosphatase into the blood. It is also elevated in children and adolescents

undergoing rapid bone growth because of bone alkaline phosphatase

and late in normal pregnancies due to the influx of placental alkaline

phosphatase.

Elevation of liver-derived alkaline phosphatase is not totally specific

for cholestasis, and a less than threefold elevation can be seen in almost

any type of liver disease. Alkaline phosphatase elevations greater than

four times normal occur primarily in patients with cholestatic liver

disorders, infiltrative liver diseases such as cancer and amyloidosis,

and bone conditions characterized by rapid bone turnover (e.g., Paget’s

disease). In bone diseases, the elevation is due to increased amounts of

the bone isoenzymes. In liver diseases, the elevation is almost always

due to increased amounts of the liver isoenzyme.

If an elevated serum alkaline phosphatase is the only abnormal

finding in an apparently healthy person or if the degree of elevation is

higher than expected in the clinical setting, identification of the source

of elevated isoenzymes is helpful (Fig. 330-1). This problem can be

approached in two ways. First, and most precise, is the fractionation

of the alkaline phosphatase by electrophoresis. The second, best substantiated, and most available approach involves the measurement of

serum 5′-nucleotidase or GGT. These enzymes are rarely elevated in

conditions other than liver disease.

In the absence of jaundice or elevated aminotransferases, an elevated

alkaline phosphatase of liver origin often, but not always, suggests early

cholestasis and, less often, hepatic infiltration by tumor or granulomata. Other conditions that cause isolated elevations of the alkaline

phosphatase include primary biliary cholangitis, sclerosing cholangitis,

Hodgkin’s disease, diabetes, hyperthyroidism, congestive heart failure,

and amyloidosis.

The level of serum alkaline phosphatase elevation is not helpful

in distinguishing between intrahepatic and extrahepatic cholestasis.

There is essentially no difference among the values found in obstructive jaundice due to cancer, common duct stone, sclerosing cholangitis,

or bile duct stricture. Values are similarly increased in patients with

intrahepatic cholestasis due to drug-induced hepatitis, primary biliary

cholangitis, sepsis, rejection of transplanted livers, and, rarely, alcoholinduced steatohepatitis. Values are also greatly elevated in hepatobiliary disorders seen in patients with AIDS (e.g., AIDS cholangiopathy

due to cytomegalovirus or cryptosporidial infection and tuberculosis

with hepatic involvement).

■ TESTS THAT MEASURE BIOSYNTHETIC

FUNCTION OF THE LIVER

Serum Albumin Serum albumin is synthesized exclusively by

hepatocytes. Serum albumin has a long half-life: 18–20 days, with ~4%

degraded per day. Because of this slow turnover, the serum albumin is

not a good indicator of acute or mild hepatic dysfunction; only minimal

changes in the serum albumin are seen in acute liver conditions such

as viral hepatitis, drug-related hepatotoxicity, and obstructive jaundice.

In hepatitis, albumin levels <3 g/dL should raise the possibility of

chronic liver disease. Hypoalbuminemia is more common in chronic

liver disorders such as cirrhosis and usually reflects severe liver damage

and decreased albumin synthesis. However, hypoalbuminemia is not

specific for liver disease and may occur in protein malnutrition of any

cause, as well as protein-losing enteropathies, nephrotic syndrome, and

chronic infections that are associated with prolonged increases in levels

of cytokines that inhibit albumin synthesis, such as serum interleukin 1

and/or tumor necrosis factor. Serum albumin should not be measured

to screen patients in whom there is no suspicion of liver disease. A

general medical clinic study of consecutive patients in whom no indications were present for albumin measurement showed that although

12% of patients had abnormal test results, the finding was of clinical

importance in only 0.4%.

Serum Globulins Serum globulins are a group of proteins made

up of γ globulins (immunoglobulins) produced by B lymphocytes and

α and β globulins produced primarily in hepatocytes. γ Globulins are

increased in chronic liver disease, such as chronic hepatitis and cirrhosis. In cirrhosis, the increased serum γ globulin concentration is due

to the increased synthesis of antibodies, some of which are directed

against intestinal bacteria. This occurs because the cirrhotic liver fails

to clear bacterial antigens that normally reach the liver through the

hepatic circulation.

Increases in the concentration of specific isotypes of γ globulins

are often helpful in the recognition of certain chronic liver diseases.

Diffuse polyclonal increases in IgG levels are common in autoimmune

hepatitis; increases >100% should alert the clinician to this possibility.

Increases in the IgM levels are common in primary biliary cholangitis,

whereas increases in the IgA levels occur in alcoholic liver disease.

■ COAGULATION FACTORS

With the exception of factor VIII, which is produced by vascular endothelial cells, the blood clotting factors are made exclusively in hepatocytes. Their serum half-lives are much shorter than albumin, ranging

from 6 h for factor VII to 5 days for fibrinogen. Because of their rapid

turnover, measurement of the clotting factors is the single best acute

measure of hepatic synthetic function and helpful in both diagnosis

and assessing the prognosis of acute parenchymal liver disease. Useful

for this purpose is the serum prothrombin time, which collectively measures factors II, V, VII, and X. Biosynthesis of factors II, VII, IX, and

X depends on vitamin K. The international normalized ratio (INR) is

used to express the degree of anticoagulation on warfarin therapy. The

INR standardizes prothrombin time measurement according to the

characteristics of the thromboplastin reagent used in a particular lab,

which is expressed as an International Sensitivity Index (ISI); the ISI is

then used in calculating the INR.

The prothrombin time may be elevated in hepatitis and cirrhosis as

well as in disorders that lead to vitamin K deficiency such as obstructive jaundice or fat malabsorption of any kind. Marked prolongation of

the prothrombin time, >5 s above control and not corrected by parenteral vitamin K administration, is a poor prognostic sign in acute viral

hepatitis and other acute and chronic liver diseases. The INR, along

with the total serum bilirubin and creatinine, are components of the

MELD score, which is used as a measure of hepatic decompensation

and to allocate organs for liver transplantation.

■ OTHER DIAGNOSTIC TESTS

Although tests may direct the physician to a category of liver disease,

additional biochemical testing, radiologic testing, and procedures are

often necessary to make the proper diagnosis, as shown in Fig. 337-1.

The most commonly used ancillary tests are reviewed here, as are the

noninvasive tests available for assessing hepatic fibrosis.

Ammonia Ammonia is produced in the body during normal

protein metabolism and by intestinal bacteria, primarily those in the

colon. The liver plays a role in the detoxification of ammonia by converting it to urea, which is excreted by the kidneys. Striated muscle also

plays a role in detoxification of ammonia, where it is combined with

glutamic acid to form glutamine. Patients with advanced liver disease

typically have significant muscle wasting, which likely contributes

to hyperammonemia. Some physicians use the blood ammonia for

detecting encephalopathy or for monitoring hepatic synthetic function,

although its use for either of these indications has problems. There

is very poor correlation between either the presence or the severity

2556 PART 10 Disorders of the Gastrointestinal System

of acute encephalopathy and elevation of blood ammonia; it can be

occasionally useful for identifying occult liver disease in patients with

mental status changes. There is also a poor correlation of the blood

serum ammonia and hepatic function. The ammonia can be elevated

in patients with severe portal hypertension and portal blood shunting

around the liver even in the presence of normal or near-normal hepatic

function. Elevated arterial ammonia levels have been shown to correlate with outcome in fulminant hepatic failure.

Liver Biopsy Percutaneous biopsy of the liver is a safe procedure

that is easily performed with local anesthesia and ultrasound

guidance. Liver biopsy is of proven value in the following situations:

(1) hepatocellular disease of uncertain cause, (2) prolonged hepatitis with

the possibility of autoimmune hepatitis, (3) unexplained hepatomegaly, (4) unexplained splenomegaly, (5) hepatic lesions uncharacterized

by radiologic imaging, (6) fever of unknown origin, and (7) staging

of malignant lymphoma. Liver biopsy is most accurate in disorders

causing diffuse changes throughout the liver and is subject to sampling error in focal disorders. Liver biopsy should not be the initial

procedure in the diagnosis of cholestasis. The biliary tree should first

be assessed for signs of obstruction. Contraindications to performing

a percutaneous liver biopsy include significant ascites and prolonged

INR. Under these circumstances, the biopsy can be performed via the

transjugular approach.

Noninvasive Tests to Detect Hepatic Fibrosis Although liver

biopsy is the standard for the assessment of hepatic fibrosis, noninvasive measures of hepatic fibrosis have been developed and show promise. These measures include multiparameter tests aimed at detecting

and staging the degree of hepatic fibrosis and imaging techniques.

FibroTest (marketed as FibroSure in the United States) is the best

evaluated of the multiparameter blood tests. The test incorporates

haptoglobin, bilirubin, GGT, apolipoprotein A-I, and α2

-macroglobulin

and has been found to have high positive and negative predictive values

for diagnosing advanced fibrosis in patients with chronic hepatitis C,

chronic hepatitis B, alcoholic liver disease, or nonalcoholic fatty liver

disease and patients taking methotrexate for psoriasis. Transient elastography (TE), marketed as FibroScan, and magnetic resonance elastography (MRE) both have gained U.S. Food and Drug Administration

approval for use in the management of patients with liver disease. TE

uses ultrasound waves to measure hepatic stiffness noninvasively. TE

has been shown to be accurate for identifying advanced fibrosis in

patients with chronic hepatitis C, primary biliary cholangitis, hemochromatosis, nonalcoholic fatty liver disease, and recurrent chronic

hepatitis after liver transplantation. MRE has been found to be superior

to TE for staging liver fibrosis in patients with a variety of chronic liver

diseases but requires access to a magnetic resonance imaging scanner

and is more expensive.

Ultrasonography Ultrasonography is the first diagnostic test

to use in patients whose liver tests suggest cholestasis, to look for

the presence of a dilated intrahepatic or extrahepatic biliary tree or

to identify gallstones. In addition, it shows space-occupying lesions

within the liver, enables the clinician to distinguish between cystic and

solid masses, and helps direct percutaneous biopsies. Ultrasound with

Doppler imaging can detect the patency of the portal vein, hepatic

artery, and hepatic veins and determine the direction of blood flow.

This is the first test ordered in patients suspected of having Budd-Chiari

syndrome.

■ USE OF LIVER TESTS

As previously noted, the best way to increase the sensitivity and specificity of laboratory tests in the detection of liver disease is to employ

a battery of tests that includes the aminotransferases, alkaline phosphatase, bilirubin, albumin, and prothrombin time along with the

judicious use of the other tests described in this chapter. Table 337-1

shows how patterns of liver tests can lead the clinician to a category

of disease that will direct further evaluation. However, it is important

to remember that no single set of liver tests will necessarily provide a

diagnosis. It is often necessary to repeat these tests on several occasions

over days to weeks for a diagnostic pattern to emerge. Figure 337-1 is

an algorithm for the evaluation of chronically abnormal liver tests.

■ GLOBAL CONSIDERATIONS

The tests and principles presented in this chapter are applicable worldwide. The causes of liver test abnormalities vary according to region. In

developing nations, infectious diseases are more commonly the etiology of abnormal serum liver tests than in developed nations.

Acknowledgment

This chapter represents a revised version of a chapter in previous editions

of Harrison’s in which Marshall M. Kaplan was a co-author.

TABLE 337-1 Liver Test Patterns in Hepatobiliary Disorders

TYPE OF DISORDER BILIRUBIN AMINOTRANSFERASES ALKALINE PHOSPHATASE ALBUMIN PROTHROMBIN TIME

Hemolysis/Gilbert’s

syndrome

Normal to 86 μmol/L (5 mg/dL)

85% due to indirect fractions

No bilirubinuria

Normal Normal Normal Normal

Acute hepatocellular

necrosis (viral, ischemic,

and drug- or toxininduced hepatitis)

Both fractions may be elevated

Peak usually follows

aminotransferases

Bilirubinuria

Elevated, often >500 IU,

ALT > AST

Normal to <3× normal

elevation

Normal Usually normal. If >5× above

control and not corrected

by parenteral vitamin K,

suggests poor prognosis

Chronic hepatocellular

disorders

Both fractions may be elevated

Bilirubinuria

Elevated, but usually

<300 IU

Normal to <3× normal

elevation

Often

decreased

Often prolonged

Fails to correct with

parenteral vitamin K

Alcoholic hepatitis,

cirrhosis

Both fractions may be elevated

Bilirubinuria

AST:ALT >2 suggests

alcoholic hepatitis or

cirrhosis

Normal to <3× normal

elevation

Often

decreased

Often prolonged

Fails to correct with

parenteral vitamin K

Intra- and extrahepatic

cholestasis (obstructive

jaundice)

Both fractions may be elevated

Bilirubinuria

Normal to moderate

elevation

Rarely >500 IU

Elevated, often >4× normal

elevation

Normal, unless

chronic

Normal

If prolonged, will correct

with parenteral vitamin K

Infiltrative diseases

(tumor, granulomata)

Usually normal Normal to slight elevation Elevated, often >4× normal

elevation

Fractionate, or confirm liver

origin with 5′-nucleotidase or

γ-glutamyl transpeptidase

Normal Normal

Abbreviations: ALT, alanine aminotransferase; AST, aspartate aminotransferase.

2557The Hyperbilirubinemias CHAPTER 338

■ FURTHER READING

Kamath PS, Kim WR: The Model for End-Stage Liver Disease

(MELD). Hepatology 45:797, 2007.

Kaplan M: Alkaline phosphatase. Gastroenterology 62:452, 1972.

Martínez SM et al: Noninvasive assessment of liver fibrosis. Hepatology 53:325, 2011.

Prati D et al: Updated definitions of healthy ranges for serum alanine

aminotransferase levels. Ann Intern Med 137:1, 2002.

338 The Hyperbilirubinemias

Allan W. Wolkoff

■ BILIRUBIN METABOLISM

The details of bilirubin metabolism are presented in Chap. 49. However, the hyperbilirubinemias are best understood in terms of perturbations of specific aspects of bilirubin metabolism and transport, and

these will be briefly reviewed here as depicted in Fig. 338-1.

Bilirubin is the end product of heme degradation. Some 70–90% of

bilirubin is derived from degradation of the hemoglobin of senescent

red blood cells. Bilirubin produced in the periphery is transported to

the liver within the plasma, where, due to its insolubility in aqueous

solutions, it is tightly bound to albumin. Under normal circumstances,

bilirubin is removed from the circulation rapidly and efficiently by

hepatocytes. Transfer of bilirubin from blood to bile involves four distinct but interrelated steps (Fig. 338-1).

1. Hepatocellular uptake: Uptake of bilirubin by the hepatocyte has

carrier-mediated kinetics. Although a number of candidate bilirubin

transporters have been proposed, the identity of the actual transporter remains elusive.

2. Intracellular binding: Within the hepatocyte, bilirubin is kept in

solution by binding as a nonsubstrate ligand to several of the glutathione-S-transferases, formerly called ligandins.

3. Conjugation: Bilirubin is conjugated with one or two glucuronic

acid moieties by a specific UDP-glucuronosyltransferase to form

bilirubin mono- and diglucuronide, respectively. Conjugation disrupts the internal hydrogen bonding that limits aqueous solubility

of bilirubin, and the resulting glucuronide conjugates are highly

soluble in water. Conjugation is obligatory for excretion of bilirubin across the bile canalicular membrane into bile. The UDPglucuronosyltransferases have been classified into gene families

based on the degree of homology among the mRNAs for the various

isoforms. Those that conjugate bilirubin and certain other substrates

have been designated the UGT1 family. These are expressed from

a single gene complex by alternative promoter usage. This gene

complex contains multiple substrate-specific first exons, designated

A1, A2, etc. (Fig. 338-2), each with its own promoter and each

encoding the amino-terminal half of a specific isoform. In addition,

there are four common exons (exons 2–5) that encode the shared

carboxyl-terminal half of all of the UGT1 isoforms. The various

first exons encode the specific aglycone substrate binding sites for

each isoform, while the shared exons encode the binding site for

the sugar donor, UDP-glucuronic acid, and the transmembrane

domain. Exon A1 and the four common exons, collectively designated as the UGT1A1 gene (Fig. 338-2), encode the physiologically

critical enzyme bilirubin-UDP-glucuronosyltransferase (UGT1A1).

A functional corollary of the organization of the UGT1 gene is that

a mutation in one of the first exons will affect only a single enzyme

isoform. By contrast, a mutation in exons 2–5 will alter all isoforms

encoded by the UGT1 gene complex.

4. Biliary excretion: It has been thought until recently that bilirubin mono- and diglucuronides are excreted directly across

the canalicular plasma membrane into the bile canaliculus by

an ATP-dependent transport process mediated by a canalicular

membrane protein called multidrug resistance–associated protein 2

(MRP2, ABCC2). Mutations of MRP2 result in the Dubin-Johnson

syndrome (see below). However, studies in patients with Rotor

syndrome (see below) indicate that after formation, a portion of

the glucuronides is transported into the portal circulation by a

sinusoidal membrane protein called multidrug resistance–associated protein 3 (MRP3, ABCC3) and is subjected to reuptake into

the hepatocyte by the sinusoidal membrane uptake transporters

organic anion transport protein 1B1 (OATP1B1, SLCO1B1) and

OATP1B3 (SLCO1B3).

■ EXTRAHEPATIC ASPECTS OF BILIRUBIN

DISPOSITION

Bilirubin in the Gut Following secretion into bile, conjugated

bilirubin reaches the duodenum and passes down the gastrointestinal tract without reabsorption by the intestinal mucosa. An appreciable fraction is converted by bacterial metabolism in the gut to

the water-soluble colorless compound urobilinogen. Urobilinogen

undergoes enterohepatic cycling. Urobilinogen not taken up by the

liver reaches the systemic circulation, from which some is cleared by

the kidneys. Unconjugated bilirubin ordinarily does not reach the gut

except in neonates or, by ill-defined alternative pathways, in the presence of severe unconjugated hyperbilirubinemia (e.g., Crigler-Najjar

syndrome, type I [CN-I]). Unconjugated bilirubin that reaches the gut

is partly reabsorbed, amplifying any underlying hyperbilirubinemia.

Renal Excretion of Bilirubin Conjugates Unconjugated bilirubin is not excreted in urine, as it is too tightly bound to albumin for

effective glomerular filtration and there is no tubular mechanism for its

renal secretion. In contrast, the bilirubin conjugates are readily filtered

at the glomerulus and can appear in urine in disorders characterized

by increased bilirubin conjugates in the circulation. It should be kept

in mind that the kidney can serve as an “overflow valve” for conjugated

bilirubin. Consequently, the level of jaundice in individuals with conjugated hyperbilirubinemia can be amplified in the presence of renal

failure.

BMG

BMG

BDG

BDG

MRP2

UCB

BT

OATP1B1

OATP1B3 ALB

UCB

Sinusoid

ALB:UCB

Space

of

Disse

UCB

+

GST

GST:UCB

MRP2

UGT1A1

UGT1A1 MRP3

BMG

BDG

FIGURE 338-1 Hepatocellular bilirubin transport. Albumin-bound bilirubin in

sinusoidal blood passes through endothelial cell fenestrae to reach the hepatocyte

surface, entering the cell by both facilitated and simple diffusional processes.

Within the cell, it is bound to glutathione-S-transferases and conjugated by

bilirubin-UDP-glucuronosyltransferase (UGT1A1) to mono- and diglucuronides,

which are actively transported across the canalicular membrane into the bile. In

addition to this direct excretion of bilirubin glucuronides, a portion are transported

into the portal circulation by MRP3 and subjected to reuptake into the hepatocyte

by OATP1B1 and OATP1B3. ALB, albumin; BDG, bilirubin diglucuronide; BMG,

bilirubin monoglucuronide; BT, proposed bilirubin transporter; GST, glutathioneS-transferase; MRP2 and MRP3, multidrug resistance–associated proteins 2 and

3; OATP1B1 and OATP1B3, organic anion transport proteins 1B1 and 1B3; UCB,

unconjugated bilirubin; UGT1A1, bilirubin-UDP-glucuronosyltransferase.

2558 PART 10 Disorders of the Gastrointestinal System

novobiocin, and rifampin, as well as various cholecystographic contrast agents,

have been reported to inhibit bilirubin uptake. The resulting unconjugated

hyperbilirubinemia resolves with cessation of the medication.

Impaired Conjugation  •  PHYSIOLOGIC NEONATAL JAUNDICE Bilirubin

produced by the fetus is cleared by the

placenta and eliminated by the maternal liver. Immediately after birth, the

neonatal liver must assume responsibility for bilirubin clearance and excretion. However, many hepatic physiologic

processes are incompletely developed at

birth. Levels of UGT1A1 are low, and

alternative excretory pathways allow passage of unconjugated bilirubin into the

gut. Since the intestinal flora that convert bilirubin to urobilinogen are also

undeveloped, an enterohepatic circulation of unconjugated bilirubin

ensues. As a consequence, most neonates develop mild unconjugated

hyperbilirubinemia between days 2 and 5 after birth. Peak levels are

typically <85–170 μmol/L (5–10 mg/dL) and decline to normal adult

concentrations within 2 weeks, as mechanisms required for bilirubin

disposition mature. Prematurity, often associated with more profound

immaturity of hepatic function and hemolysis, can result in higher levels of unconjugated hyperbilirubinemia. A rapidly rising unconjugated

bilirubin concentration, or absolute levels >340 μmol/L (20 mg/dL),

puts the infant at risk for bilirubin encephalopathy, or kernicterus.

Under these circumstances, bilirubin crosses an immature blood-brain

barrier and precipitates in the basal ganglia and other areas of the

brain. The consequences range from appreciable neurologic deficits to

death. Treatment options include phototherapy, which converts bilirubin into water-soluble photoisomers that are excreted directly into bile,

and exchange transfusion. The canalicular mechanisms responsible for

bilirubin excretion are also immature at birth, and their maturation

may lag behind that of UGT1A1; this can lead to transient conjugated

neonatal hyperbilirubinemia, especially in infants with hemolysis.

ACQUIRED CONJUGATION DEFECTS A modest reduction in bilirubin

conjugating capacity may be observed in advanced hepatitis or cirrhosis. However, in this setting, conjugation is better preserved than other

aspects of bilirubin disposition, such as canalicular excretion. Various

drugs, including pregnanediol, novobiocin, chloramphenicol, gentamicin, and atazanavir, may produce unconjugated hyperbilirubinemia by

inhibiting UGT1A1 activity. Bilirubin conjugation may be inhibited

by certain fatty acids that are present in breast milk, but not serum,

of mothers whose infants have excessive neonatal hyperbilirubinemia

(breast milk jaundice). Alternatively, there may be increased enterohepatic circulation of bilirubin in these infants. The pathogenesis of

breast milk jaundice appears to differ from that of transient familial

neonatal hyperbilirubinemia (Lucey-Driscoll syndrome), in which

there may be a UGT1A1 inhibitor in maternal serum.

■ HEREDITARY DEFECTS IN BILIRUBIN

CONJUGATION

Three familial disorders characterized by differing degrees of unconjugated hyperbilirubinemia have long been recognized. The defining

clinical features of each are described below (Table 338-1). While these

disorders have been recognized for decades to reflect differing degrees

of deficiency in the ability to conjugate bilirubin, recent advances in

the molecular biology of the UGT1 gene complex have elucidated their

interrelationships and clarified previously puzzling features.

Crigler-Najjar Syndrome, Type I CN-I is characterized by striking unconjugated hyperbilirubinemia of ∼340–765 μmol/L (20–45 mg/

dL) that appears in the neonatal period and persists for life. Other conventional hepatic biochemical tests such as serum aminotransferases

500 kb

A13 A12 A11 A10 A9 A8 A7 A6 A5 A4 A3 A2 A1

Common Exons

2 3 4 5

~286 AA ~245 AA

TATA Box

A(TA)6TAA

Variable (Substrate Specific) First Exons

5′ 3′

FIGURE 338-2 Structural organization of the human UGT1 gene complex. This large complex on chromosome 2 contains

at least 13 substrate-specific first exons (A1, A2, etc.). Since four of these are pseudogenes, nine UGT1 isoforms with

differing substrate specificities are expressed. Each exon 1 has its own promoter and encodes the amino-terminal

substrate-specific ∼286 amino acids of the various UGT1-encoded isoforms, and common exons 2–5 encode the 245

carboxyl-terminal amino acids common to all of the isoforms. mRNAs for specific isoforms are assembled by splicing a

particular first exon such as the bilirubin-specific exon A1 to exons 2 to 5. The resulting message encodes a complete

enzyme, in this particular case, bilirubin-UDP-glucuronosyltransferase (UGT1A1). Mutations in a first exon affect only a

single isoform. Those in exons 2–5 affect all enzymes encoded by the UGT1 complex.

DISORDERS OF BILIRUBIN METABOLISM

LEADING TO UNCONJUGATED

HYPERBILIRUBINEMIA

■ INCREASED BILIRUBIN PRODUCTION

Hemolysis Increased destruction of erythrocytes leads to increased

bilirubin turnover and unconjugated hyperbilirubinemia; the hyperbilirubinemia is usually modest in the presence of normal liver function.

In particular, the bone marrow is only capable of a sustained eightfold

increase in erythrocyte production in response to a hemolytic stress.

Therefore, hemolysis alone cannot result in a sustained hyperbilirubinemia of more than ∼68 μmol/L (4 mg/dL). Higher values imply concomitant hepatic dysfunction. When hemolysis is the only abnormality

in an otherwise healthy individual, the result is a purely unconjugated

hyperbilirubinemia, with the direct-reacting fraction as measured in a

typical clinical laboratory being ≤15% of the total serum bilirubin. In

the presence of systemic disease, which may include a degree of hepatic

dysfunction, hemolysis may produce a component of conjugated

hyperbilirubinemia in addition to an elevated unconjugated bilirubin

concentration. Prolonged hemolysis may lead to the precipitation of

bilirubin salts within the gallbladder or biliary tree, resulting in the formation of gallstones in which bilirubin, rather than cholesterol, is the

major component. Such pigment stones may lead to acute or chronic

cholecystitis, biliary obstruction, or any other biliary tract consequence

of calculous disease.

Ineffective Erythropoiesis During erythroid maturation, small

amounts of hemoglobin may be lost at the time of nuclear extrusion,

and a fraction of developing erythroid cells is destroyed within the

marrow. These processes normally account for a small proportion of

bilirubin that is produced. In various disorders, including thalassemia

major, megaloblastic anemias due to folate or vitamin B12 deficiency,

congenital erythropoietic porphyria, lead poisoning, and various

congenital and acquired dyserythropoietic anemias, the fraction of

total bilirubin production derived from ineffective erythropoiesis is

increased, reaching as much as 70% of the total. This may be sufficient

to produce modest degrees of unconjugated hyperbilirubinemia.

Miscellaneous Degradation of the hemoglobin of extravascular collections of erythrocytes, such as those seen in massive tissue

infarctions or large hematomas, may lead transiently to unconjugated

hyperbilirubinemia.

■ DECREASED HEPATIC BILIRUBIN CLEARANCE

Decreased Hepatic Uptake Decreased hepatic bilirubin uptake

is believed to contribute to the unconjugated hyperbilirubinemia of

Gilbert’s syndrome (GS), although the molecular basis for this finding

remains unclear (see below). Several drugs, including flavaspidic acid,

2559The Hyperbilirubinemias CHAPTER 338

and alkaline phosphatase are normal, and there is no evidence of

hemolysis. Hepatic histology is also essentially normal except for the

occasional presence of bile plugs within canaliculi. Bilirubin glucuronides are virtually absent from the bile, and there is no detectable

constitutive expression of UGT1A1 activity in hepatic tissue. Neither

UGT1A1 activity nor the serum bilirubin concentration responds to

administration of phenobarbital or other enzyme inducers. Unconjugated bilirubin accumulates in plasma, from which it is eliminated very

slowly by alternative pathways that include direct passage into the bile

and small intestine, possibly via bilirubin photoisomers. This accounts

for the small amount of urobilinogen found in feces. No bilirubin is

found in the urine. First described in 1952, the disorder is rare (estimated prevalence, 0.6–1.0 per million). Many patients are from geographically or socially isolated communities in which consanguinity is

common, and pedigree analyses show an autosomal recessive pattern

of inheritance. The majority of patients (type IA) exhibit defects in

the glucuronide conjugation of a spectrum of substrates in addition to

bilirubin, including various drugs and other xenobiotics. These individuals have mutations in one of the common exons (2–5) of the UGT1

gene (Fig. 338-2). In a smaller subset (type IB), the defect is limited

largely to bilirubin conjugation, and the causative mutation is in the

bilirubin-specific exon A1. Estrogen glucuronidation is mediated by

UGT1A1 and is defective in all CN-I patients. More than 30 different

genetic lesions of UGT1A1 responsible for CN-I have been identified,

including deletions, insertions, alterations in intron splice donor and

acceptor sites, exon skipping, and point mutations that introduce

premature stop codons or alter critical amino acids. Their common

feature is that they all encode proteins with absent or, at most, traces of

bilirubin-UDP-glucuronosyltransferase enzymatic activity.

Prior to the use of phototherapy, most patients with CN-I died of

bilirubin encephalopathy (kernicterus) in infancy or early childhood.

A few lived as long as early adult life without overt neurologic damage,

although more subtle testing usually indicated mild but progressive

brain damage. In the absence of liver transplantation, death eventually

supervened from late-onset bilirubin encephalopathy, which often followed a nonspecific febrile illness. Although isolated hepatocyte transplantation has been used in a small number of cases of CN-I, early liver

transplantation (Chap. 345) remains the best hope to prevent brain

injury and death at present. It is anticipated that gene replacement

therapy may be an option in the future.

Crigler-Najjar Syndrome, Type II (CN-II) This condition

was recognized as a distinct entity in 1962 and is characterized by

marked unconjugated hyperbilirubinemia in the absence of abnormalities of other conventional hepatic biochemical tests, hepatic

histology, or hemolysis. It differs from CN-I in several specific ways

(Table 338-1): (1) although there is considerable overlap, average

bilirubin concentrations are lower in CN-II; (2) accordingly, CN-II is

only infrequently associated with kernicterus; (3) bile is deeply colored,

and bilirubin glucuronides are present, with a striking, characteristic

increase in the proportion of monoglucuronides; (4) UGT1A1 in liver

is usually present at reduced levels (typically ≤10% of normal); and (5)

while typically detected in infancy, hyperbilirubinemia was not recognized in some cases until later in life and, in one instance, at age 34. As

with CN-I, most CN-II cases exhibit abnormalities in the conjugation

of other compounds, such as salicylamide and menthol, but in some

instances, the defect appears limited to bilirubin. Reduction of serum

bilirubin concentrations by >25% in response to enzyme inducers

such as phenobarbital distinguishes CN-II from CN-I, although this

response may not be elicited in early infancy and often is not accompanied by measurable UGT1A1 induction. Bilirubin concentrations

during phenobarbital administration do not return to normal but are

typically in the range of 51–86 μmol/L (3–5 mg/dL). Although the

incidence of kernicterus in CN-II is low, instances have occurred, not

only in infants but also in adolescents and adults, often in the setting

of an intercurrent illness, fasting, or another factor that temporarily

raises the serum bilirubin concentration above baseline and reduces

serum albumin levels. For this reason, phenobarbital therapy is widely

recommended, a single bedtime dose often sufficing to maintain clinically safe serum bilirubin concentrations.

Over 100 different mutations in the UGT1 gene have been identified as causing CN-I or CN-II. It was found that missense mutations

are more common in CN-II patients, as would be expected in this

less severe phenotype. Their common feature is that they encode for

a bilirubin-UDP-glucuronosyltransferase with markedly reduced, but

detectable, enzymatic activity. The spectrum of residual enzyme activity explains the spectrum of phenotypic severity of the resulting hyperbilirubinemia. Molecular analysis has established that a large majority

of CN-II patients are either homozygotes or compound heterozygotes

for CN-II mutations and that individuals carrying one mutated and

one entirely normal allele have normal bilirubin concentrations.

Gilbert Syndrome This syndrome is characterized by mild unconjugated hyperbilirubinemia, normal values for standard hepatic biochemical tests, and normal hepatic histology other than a modest

increase of lipofuscin pigment in some patients. Serum bilirubin

concentrations are most often <51 μmol/L (<3 mg/dL), although

both higher and lower values are frequent. The clinical spectrum of

hyperbilirubinemia fades into that of CN-II at serum bilirubin concentrations of 86–136 μmol/L (5–8 mg/dL). At the other end of the scale,

the distinction between mild cases of GS and a normal state is often

blurred. Bilirubin concentrations may fluctuate substantially in any

given individual, and at least 25% of patients will exhibit temporarily

normal values during prolonged follow-up. More elevated values are

TABLE 338-1 Principal Differential Characteristics of Gilbert and Crigler-Najjar Syndromes

FEATURE 

CRIGLER-NAJJAR SYNDROME

TYPE I TYPE II GILBERT SYNDROME 

Total serum bilirubin, μmol/L (mg/dL) 310–755 (usually >345) (18–45

[usually >20])

100–430 (usually ≤345) (6–25 [usually

≤20])

Typically ≤70 μmol/L (≤4 mg/dL) in

absence of fasting or hemolysis

Routine liver tests

Response to phenobarbital

Kernicterus

Hepatic histology

Normal

None

Usual

Normal

Normal

Decreases bilirubin by >25%

Rare

Normal

Normal

Decreases bilirubin to normal

No

Usually normal; increased lipofuscin

pigment in some

Bile characteristics

Color

Bilirubin fractions

Pale or colorless

>90% unconjugated

Pigmented

Largest fraction (mean: 57%)

monoconjugates

Normal dark color

Mainly diconjugates but

monoconjugates increased (mean: 23%)

Bilirubin UDP-glucuronosyltransferase

activity

Inheritance (all autosomal)

Typically absent; traces in some

patients

Recessive

Markedly reduced: 0–10% of normal

Predominantly recessive

Reduced: typically 10–33% of normal

Promoter mutation: recessive

Missense mutations: 7 of 8 dominant;

1 reportedly recessive

2560 PART 10 Disorders of the Gastrointestinal System

associated with stress, fatigue, alcohol use, reduced caloric intake,

and intercurrent illness, while increased caloric intake or administration of enzyme-inducing agents produces lower bilirubin levels.

GS is most often diagnosed at or shortly after puberty or in adult life

during routine examinations that include multichannel biochemical

analyses. UGT1A1 activity is typically reduced to 10–35% of normal,

and bile pigments exhibit a characteristic increase in bilirubin monoglucuronides. Studies of radiobilirubin kinetics indicate that hepatic

bilirubin clearance is reduced to an average of one-third of normal.

Administration of phenobarbital normalizes both the serum bilirubin concentration and hepatic bilirubin clearance; however, failure

of UGT1A1 activity to improve in many such instances suggests the

possible coexistence of an additional defect. Compartmental analysis

of bilirubin kinetic data suggests that GS patients may have a defect in

bilirubin uptake as well as in conjugation, although this has not been

shown directly. Defects in the hepatic uptake of other organic anions

that at least partially share an uptake mechanism with bilirubin, such

as sulfobromophthalein and indocyanine green (ICG), are observed

in a minority of patients. The metabolism and transport of bile acids

that do not utilize the bilirubin uptake mechanism are normal. The

magnitude of changes in the serum bilirubin concentration induced

by provocation tests such as 48 h of fasting or the IV administration

of nicotinic acid has been reported to be of help in separating GS

patients from normal individuals. Other studies dispute this assertion.

Moreover, on theoretical grounds, the results of such studies should

provide no more information than simple measurements of the baseline serum bilirubin concentration. Family studies indicate that GS

and hereditary hemolytic anemias such as hereditary spherocytosis,

glucose-6-phosphate dehydrogenase deficiency, and β-thalassemia trait

sort independently. Reports of hemolysis in up to 50% of GS patients

are believed to reflect better case finding, since patients with both GS

and hemolysis have higher bilirubin concentrations and are more likely

to be jaundiced than patients with either defect alone.

GS is common, with many series placing its prevalence as high

as 8%. Males predominate over females by reported ratios ranging

from 1.5:1 to >7:1. However, these ratios may have a large artifactual

component since normal males have higher mean bilirubin levels than

normal females, but the diagnosis of GS is often based on comparison

to normal ranges established in men. The high prevalence of GS in the

general population may explain the reported frequency of mild unconjugated hyperbilirubinemia in liver transplant recipients. The disposition of most xenobiotics metabolized by glucuronidation appears to

be normal in GS, as is oxidative drug metabolism in the majority of

reported studies. The principal exception is the metabolism of the antitumor agent irinotecan (CPT-11), whose active metabolite (SN-38) is

glucuronidated specifically by bilirubin-UDP-glucuronosyltransferase.

Administration of CPT-11 to patients with GS has resulted in several

toxicities, including intractable diarrhea and myelosuppression. Some

reports also suggest abnormal disposition of menthol, estradiol benzoate, acetaminophen, tolbutamide, and rifamycin SV. Although some

of these studies have been disputed, and there have been no reports of

clinical complications from use of these agents in GS, prudence should

be exercised in prescribing them or any agents metabolized primarily

by glucuronidation in this condition. It should also be noted that the

HIV protease inhibitors indinavir and atazanavir (Chap. 202) can

inhibit UGT1A1, resulting in hyperbilirubinemia that is most pronounced in patients with preexisting GS.

Most older pedigree studies of GS were consistent with autosomal

dominant inheritance with variable expressivity. However, studies of

the UGT1 gene in GS have indicated a variety of molecular genetic

bases for the phenotypic picture and several different patterns of

inheritance. Studies in Europe and the United States found that nearly

all patients had normal coding regions for UGT1A1 but were homozygous for the insertion of an extra TA (i.e., A[TA]7

TAA rather than

A[TA]6

TAA) in the promoter region of the first exon. This appeared

to be necessary, but not sufficient, for clinically expressed GS, since

15% of normal controls were also homozygous for this variant. While

normal by standard criteria, these individuals had somewhat higher

bilirubin concentrations than the rest of the controls studied. Heterozygotes for this abnormality had bilirubin concentrations identical

to those homozygous for the normal A[TA]6

TAA allele. The prevalence

of the A[TA]7

TAA allele in a general Western population is 30%, in

which case 9% would be homozygotes. This is slightly higher than

the prevalence of GS based on purely phenotypic parameters. It was

suggested that additional variables, such as mild hemolysis or a defect

in bilirubin uptake, might be among the factors enhancing phenotypic

expression of the defect.

Phenotypic expression of GS due solely to the A[TA]7

TAA promoter

abnormality is inherited as an autosomal recessive trait. A number of

CN-II kindreds have been identified in whom there is also an allele

containing a normal coding region but the A[TA]7

TAA promoter

abnormality. CN-II heterozygotes, who have the A[TA]6

TAA promoter, are phenotypically normal, whereas those with the A[TA]7

TAA

promoter express the phenotypic picture of GS. GS in such kindreds

may also result from homozygosity for the A[TA]7

TAA promoter

abnormality. Seven different missense mutations in the UGT1 gene

that reportedly cause GS with dominant inheritance have been found

in Japanese individuals. Another Japanese patient with mild unconjugated hyperbilirubinemia was homozygous for a missense mutation in

exon 5. GS in her family appeared to be recessive.

DISORDERS OF BILIRUBIN METABOLISM

LEADING TO MIXED OR PREDOMINANTLY

CONJUGATED HYPERBILIRUBINEMIA

In hyperbilirubinemia due to acquired liver disease (e.g., acute hepatitis, common bile duct stone), there are usually elevations in the

serum concentrations of both conjugated and unconjugated bilirubin.

Although biliary tract obstruction or hepatocellular cholestatic injury

may present on occasion with a predominantly conjugated hyperbilirubinemia, it is generally not possible to differentiate intrahepatic

from extrahepatic causes of jaundice based on the serum levels or

relative proportions of unconjugated and conjugated bilirubin. The

major reason for determining the amounts of conjugated and unconjugated bilirubin in the serum is for the initial differentiation of

hepatic parenchymal and obstructive disorders (mixed conjugated and

unconjugated hyperbilirubinemia) from the inheritable and hemolytic disorders discussed above that are associated with unconjugated

hyperbilirubinemia.

■ FAMILIAL DEFECTS IN HEPATIC

EXCRETORY FUNCTION

Dubin-Johnson Syndrome (DJS) This benign, relatively rare

disorder is characterized by low-grade, predominantly conjugated

hyperbilirubinemia (Table 338-2). Total bilirubin concentrations are

typically between 34 and 85 μmol/L (2 and 5 mg/dL) but on occasion

can be in the normal range or as high as 340–430 μmol/L (20–25 mg/dL)

and can fluctuate widely in any given patient. The degree of hyperbilirubinemia may be increased by intercurrent illness, oral contraceptive use, and pregnancy. Because the hyperbilirubinemia is due to

a predominant rise in conjugated bilirubin, bilirubinuria is characteristically present. Aside from elevated serum bilirubin levels, other

routine laboratory tests are normal. Physical examination is usually

normal except for jaundice, although an occasional patient may have

hepatosplenomegaly.

Patients with DJS are usually asymptomatic, although some may

have vague constitutional symptoms. These latter patients have usually

undergone extensive diagnostic examinations for unexplained jaundice and have high levels of anxiety. In women, the condition may be

subclinical until the patient becomes pregnant or receives oral contraceptives, at which time chemical hyperbilirubinemia becomes frank

jaundice. Even in these situations, other routine liver function tests,

including serum alkaline phosphatase and transaminase activities, are

normal.

A cardinal feature of DJS is the accumulation of dark, coarsely granular pigment in the lysosomes of centrilobular hepatocytes. As a result,

the liver may be grossly black in appearance. This pigment is thought

to be derived from epinephrine metabolites that are not excreted normally. The pigment may disappear during bouts of viral hepatitis, only

to reaccumulate slowly after recovery.

2561The Hyperbilirubinemias CHAPTER 338

Biliary excretion of a number of anionic compounds is compromised in DJS. These include various cholecystographic agents, as

well as sulfobromophthalein (Bromsulphalein [BSP]), a synthetic

dye formerly used in a test of liver function. In this test, the rate of

disappearance of BSP from plasma was determined following bolus

IV administration. BSP is conjugated with glutathione in the hepatocyte; the resulting conjugate is normally excreted rapidly into the bile

canaliculus. Patients with DJS exhibit characteristic rises in plasma

concentrations at 90 min after injection, due to reflux of conjugated

BSP into the circulation from the hepatocyte. Dyes such as ICG that

are taken up by hepatocytes but are not further metabolized prior to

biliary excretion do not show this reflux phenomenon. Continuous

BSP infusion studies suggest a reduction in the time to maximum

plasma concentration (t

max) for biliary excretion. Bile acid disposition,

including hepatocellular uptake and biliary excretion, is normal in DJS.

These patients have normal serum and biliary bile acid concentrations

and do not have pruritus.

By analogy with findings in several mutant rat strains, the selective

defect in biliary excretion of bilirubin conjugates and certain other

classes of organic compounds, but not of bile acids, that characterizes

DJS in humans was found to reflect defective expression of MRP2

(ABCC2), an ATP-dependent canalicular membrane transporter. Several different mutations in the ABCC2 gene produce the Dubin-Johnson

phenotype, which has an autosomal recessive pattern of inheritance.

Although MRP2 is undoubtedly important in the biliary excretion of

conjugated bilirubin, the fact that this pigment is still excreted in the

absence of MRP2 suggests that other, as yet uncharacterized, transport

proteins may serve in a secondary role in this process.

Patients with DJS also have a diagnostic abnormality in urinary

coproporphyrin excretion. There are two naturally occurring coproporphyrin isomers, I and III. Normally, ∼75% of the coproporphyrin

in urine is isomer III. In urine from DJS patients, total coproporphyrin content is normal, but >80% is isomer I. Heterozygotes for the

syndrome show an intermediate pattern. The molecular basis for this

phenomenon remains unclear.

Rotor Syndrome (RS) This benign, autosomal recessive disorder

is clinically similar to DJS (Table 338-2), although it is seen even less

frequently. A major phenotypic difference is that the liver in patients

with RS has no increased pigmentation and appears totally normal.

The only abnormality in routine laboratory tests is an elevation of total

serum bilirubin, due to a predominant rise in conjugated bilirubin.

This is accompanied by bilirubinuria. Several additional features differentiate RS from DJS. In RS, the gallbladder is usually visualized on oral

cholecystography, in contrast to the nonvisualization that is typical of

DJS. The pattern of urinary coproporphyrin excretion also differs. The

pattern in RS resembles that of many acquired disorders of hepatobiliary function, in which coproporphyrin I, the major coproporphyrin

isomer in bile, refluxes from the hepatocyte back into the circulation

and is excreted in urine. Thus, total urinary coproporphyrin excretion

is substantially increased in RS, in contrast to the normal levels seen in

DJS. Although the fraction of coproporphyrin I in urine is elevated, it

is usually <70% of the total, compared with ≥80% in DJS. The disorders

also can be distinguished by their patterns of BSP excretion. Although

clearance of BSP from plasma is delayed in RS, there is no reflux of

conjugated BSP back into the circulation as seen in DJS. Kinetic analysis of plasma BSP infusion studies suggests the presence of a defect

in intrahepatocellular storage of this compound. This has never been

demonstrated directly. Recent studies indicate that the molecular

basis of RS results from simultaneous deficiency of the hepatocyte

plasma membrane transporters OATP1B1 (SLCO1B1) and OATP1B3

(SLCO1B3). This results in reduced reuptake by these transporters of

conjugated bilirubin that has been pumped out of the hepatocyte into

the portal circulation by MRP3 (ABCC3) (Fig. 338-1).

Benign Recurrent Intrahepatic Cholestasis (BRIC) This

rare disorder is characterized by recurrent attacks of pruritus and

jaundice. The typical episode begins with mild malaise and elevations

in serum aminotransferase levels, followed rapidly by rises in alkaline

phosphatase and conjugated bilirubin and onset of jaundice and itching. The first one or two episodes may be misdiagnosed as acute viral

hepatitis. The cholestatic episodes, which may begin in childhood

or adulthood, can vary in duration from several weeks to months,

followed by a complete clinical and biochemical resolution. Intervals

between attacks may vary from several months to years. Between

episodes, physical examination is normal, as are serum levels of bile

acids, bilirubin, transaminases, and alkaline phosphatase. The disorder

is familial and has an autosomal recessive pattern of inheritance. BRIC

is considered a benign disorder in that it does not lead to cirrhosis or

end-stage liver disease. However, the episodes of jaundice and pruritus

can be prolonged and debilitating, and some patients have undergone

liver transplantation to relieve the intractable and disabling symptoms.

Treatment during the cholestatic episodes is symptomatic; there is no

specific treatment to prevent or shorten the occurrence of episodes.

A gene termed FIC1 was recently identified and found to be mutated

in patients with BRIC. Curiously, this gene is expressed strongly in

the small intestine but only weakly in the liver. The protein encoded

by FIC1 shows little similarity to those that have been shown to play

a role in bile canalicular excretion of various compounds. Rather, it

appears to be a member of a P-type ATPase family that transports

aminophospholipids from the outer to the inner leaflet of a variety of

cell membranes. Its relationship to the pathobiology of this disorder

remains unclear. A second phenotypically identical form of BRIC,

termed BRIC type 2, has been described resulting from mutations in

the bile salt excretory protein (BSEP), the protein that is defective in

progressive familial intrahepatic cholestasis (PFIC) type 2 (Table 338-2).

How some mutations in this protein result in the episodic BRIC phenotype is unknown.

Progressive Familial Intrahepatic Cholestasis This name is

applied to three phenotypically related syndromes (Table 338-2). PFIC

type 1 (Byler’s disease) presents in early infancy as cholestasis that

TABLE 338-2 Principal Differential Characteristics of Inheritable Disorders of Bile Canalicular Function

DJS ROTOR PFIC1 BRIC1 PFIC2 BRIC2 PFIC3

Gene

Protein

Cholestasis

ABCCA

MRP2

No

SLCO1B1/SLCO1B3

OATP1B1/1B3

No

ATP8B1

FIC1

Yes

ATP8B1

FIC1

Episodic

ABCB11

BSEP

Yes

ABCB11

BSEP

Episodic

ABCB4

MDR3

Yes

Serum GGT

Serum bile

acids

Normal

Normal

Normal

Normal

Normal

↑↑

Normal

↑↑ during

episodes

Normal

↑↑

Normal

↑↑ during

episodes

↑↑

↑↑

Clinical

features

Mild conjugated

hyperbilirubinemia;

otherwise, normal liver

function; dark pigment

in liver; characteristic

pattern of urinary

coproporphyrins

Mild conjugated

hyperbilirubinemia;

otherwise, normal

liver function; liver

without abnormal

pigmentation

Severe cholestasis

beginning in

childhood

Recurrent

episodes of

cholestasis

beginning at any

age

Severe cholestasis

beginning in

childhood

Recurrent

episodes of

cholestasis

beginning at any

age

Severe

cholestasis

beginning in

childhood;

decreased

phospholipids

in bile

Abbreviations: BRIC, benign recurrent intrahepatic cholestasis; BSEP, bile salt excretory protein; DJS, Dubin-Johnson syndrome; GGT, γ-glutamyl transferase; MRP2,

multidrug resistance–associated protein 2; OATP1A/1B, organic anion transport proteins 1B1 and 1B3; PFIC, progressive familial intrahepatic cholestasis; ↑↑, increased.