The Hyperbilirubinemias¶
Chapter 349 | Part 10: Disorders of the Gastrointestinal System
KEY CLINICAL POINTS¶
- Hyperbilirubinemias result from disruptions in bilirubin metabolism, transport, or excretion, categorized as unconjugated, conjugated, or mixed.
- Gilbert syndrome (GS) is the most common unconjugated hyperbilirubinemia, characterized by mild elevations in serum bilirubin with normal liver function.
- Crigler-Najjar syndrome (CN-I and CN-II) involves severe congenital defects in bilirubin conjugation, requiring phototherapy or liver transplantation.
- Dubin-Johnson syndrome (DJS) and Rotor syndrome are benign disorders of bilirubin excretion, with DJS showing hepatic pigment accumulation and RS involving impaired canalicular transport.
- Diagnosis relies on liver function tests, bilirubin fractionation, and genetic testing, with management tailored to the underlying pathophysiology.
1. DEFINITION & OVERVIEW¶
Hyperbilirubinemias refer to elevated serum bilirubin levels due to impaired hepatic uptake, conjugation, or excretion. They are classified as unconjugated (prehepatic, hemolytic), conjugated (posthepatic, obstructive), or mixed (hepatic dysfunction). Bilirubin metabolism involves uptake, conjugation by UDP-glucuronosyltransferase (UGT1A1), and biliary excretion via MRP2 and OATP transporters.
Table 348-1: Liver Test Patterns in Hepatobiliary Disorders¶
| TYPE OF DISORDER | BILIRUBIN | AMINOTRANSF ERASES | ALKALINE PHO SPHATASE | ALBUMIN | PROTHROMBIN TIME |
|---|---|---|---|---|---|
| Hemolysis/Gilber t’s syndrome | Normal to 86 mmol/L (5 mg/dL) (85% indirect) | Normal | Normal | Normal | Normal |
| Acute hepatocellular necrosis | Both fractions elevated | Elevated (>500 IU/L) | Normal to <3× normal | Normal | Usually normal |
| Chronic hepatocellular disorders | Both fractions elevated | Elevated (<300 IU/L) | Often decreased | Often prolonged | Fails to correct with vitamin K |
| Intra- and extrahepatic cholestasis | Both fractions elevated | Normal to moderate elevation | Elevated (>4× normal) | Normal | If prolonged, corrects with vitamin K |
| Infiltrative diseases | Usually normal | Normal to slight elevation | Elevated (>4× normal) | Normal | Normal |
1.1 Bilirubin Metabolism¶
Bilirubin is derived from heme degradation, with 70–90% originating from senescent red blood cells. Unconjugated bilirubin is transported to the liver, conjugated with glucuronic acid by UGT1A1, and excreted into bile. Conjugated bilirubin is water-soluble and excreted via canalicular transporters (MRP2, OATP1B1/1B3).
1.2 Classification¶
Disorders are categorized by etiology: hemolysis (Gilbert syndrome), hepatic dysfunction (acute/chronic hepatitis), obstructive jaundice, or genetic defects in UGT1A1 (CN-I/II) or transporters (DJS, RS).
2. EPIDEMIOLOGY¶
Gilbert syndrome (GS) is the most common unconjugated hyperbilirubinemia, with prevalence up to 8% in males. Crigler-Najjar syndrome (CN-I) is rare (0.6–1.0 per million), while DJS and Rotor syndrome are also rare. Hemolytic disorders (e.g., thalassemia) and drug-induced hyperbilirubinemia are more common in certain populations.
2.1 Risk Factors¶
Genetic mutations in UGT1A1 (CN-I/II), MRP2 (DJS), or OATP1B1/1B3 (RS). Hemolysis, liver disease, and drug interactions (e.g., phenobarbital, rifampin) increase risk.
3. ETIOLOGY & PATHOPHYSIOLOGY¶
Disorders arise from defects in bilirubin uptake, conjugation, or excretion. UGT1A1 mutations (CN-I/II), MRP2 dysfunction (DJS), or OATP1B1/1B3 deficiency (RS) are genetic causes. Acquired causes include liver disease, hemolysis, or drug interference with conjugation.
Table 349-1: Principal Differential Characteristics of Gilbert and Crigler-Najjar Syndromes¶
| FEATURE | CRIGLER-NAJJAR SYNDROME | GILBERT SYNDROME |
|---|---|---|
| Total serum bilirubin (mmol/L) | 310–755 (usually >345) [usually >20] | Typically £70 mmol/L (£4 mg/dL) |
| Routine liver tests | Normal | Normal |
| Response to phenobarbital | None | Decreases bilirubin to normal |
| Kernicterus | Usual | No |
| Bile characteristics | Pale or colorless (>90% unconjugated) | Normal dark color (mainly diconjugates) |
| UGT1A1 activity | Typically absent | Reduced (10–33% of normal) |
3.1 UGT1A1 Mutations¶
CN-I: Complete absence of UGT1A1 activity. CN-II: Partial deficiency (10–30% of normal). GS: Reduced UGT1A1 activity (10–33% of normal) with variable expressivity.
3.2 Transport Defects¶
DJS: MRP2 deficiency impairs biliary excretion. RS: OATP1B1/1B3 deficiency reduces conjugated bilirubin reuptake. BRIC: BSEP (ABCB11) mutations cause episodic cholestasis.
4. CLINICAL FEATURES¶
Unconjugated hyperbilirubinemia presents with jaundice, fatigue, and mild elevations in bilirubin without liver dysfunction. Conjugated hyperbilirubinemia (DJS, RS) may cause dark urine, pruritus, and hepatic pigment deposition. Severe cases (CN-I) risk kernicterus in neonates.
4.1 Gilbert Syndrome¶
Asymptomatic, with mild unconjugated hyperbilirubinemia ( ≤ 345 µ mol/L). Jaundice may worsen with fasting, stress, or illness.
4.2 Crigler-Najjar Syndrome¶
Severe unconjugated hyperbilirubinemia (>340 µ mol/L) with kernicterus risk. CN-I is life-threatening; CN-II responds partially to phenobarbital.
4.3 Dubin-Johnson Syndrome¶
Mild conjugated hyperbilirubinemia (34–85 µ mol/L) with hepatic pigment deposition. Jaundice is persistent but nonprogressive.
5. DIFFERENTIAL DIAGNOSIS¶
Differentiate between hemolytic anemia, liver disease, obstructive jaundice, and genetic disorders. Key features include bilirubin fractionation, liver function tests, and urinary coproporphyrin patterns.
5.1 Hemolysis vs. Hepatic Dysfunction¶
Hemolysis shows elevated indirect bilirubin and normal conjugated fractions. Hepatic dysfunction (e.g., cholestasis) elevates both fractions.
5.2 Genetic Disorders¶
CN-I/II: Severe unconjugated hyperbilirubinemia with normal liver tests. DJS/RS: Conjugated hyperbilirubinemia with normal liver enzymes.
6. INVESTIGATIONS & DIAGNOSIS¶
Diagnosis involves serum bilirubin fractionation (direct/indirect), liver function tests, and genetic testing. Urinary coproporphyrin analysis and BSP excretion studies help distinguish syndromes.
Table 349-2: Principal Differential Characteristics of Inheritable Disorders of Bile Canalicular Function¶
| FEATURE | DJS | ROTOR | PFIC1 | BRIC1 | PFIC2 | BRIC2 | PFIC3 |
|---|---|---|---|---|---|---|---|
| Gene | ABCCA | SLCO1B1/ SLCO1B3 | ATP8B1 | ATP8B1 | ABCB11 | ABCB11 | ABCB4 |
| Protein | MRP2 | OATP1B1/1 B3 | FIC1 | FIC1 | BSEP | BSEP | MDR3 |
| Cholestasis | No | No | Yes | Episodic | Yes | Episodic | Yes |
| Serum GGT | Normal | Normal | Normal | Normal | ›› | ›› | Normal |
| Serum bile acids | Normal | Normal | ›› | ›› during episodes | ›› | ›› during episodes | ›› |
| FEATURE | DJS | ROTOR | PFIC1 | BRIC1 | PFIC2 | BRIC2 | PFIC3 |
|---|---|---|---|---|---|---|---|
| Clinical features | Mild conjugated hyperbilirub inemia | Mild conjugated hyperbilirub inemia | Severe cholestasis | Recurrent episodes | Severe cholestasis | Recurrent episodes | Severe cholestasis |
6.1 Laboratory Tests¶
Serum bilirubin (total, direct, indirect), alkaline phosphatase, transaminases, and prothrombin time. Urinary coproporphyrin isomer analysis (isomer I in DJS, isomer III in GS).
6.2 Imaging¶
Ultrasound or MRI to assess biliary obstruction. Liver biopsy may show hepatic pigment in DJS or cholestasis in PFIC.
7. MANAGEMENT & TREATMENT¶
Management depends on the underlying cause. Phototherapy, phenobarbital, or liver transplantation are used for severe cases. Supportive care includes hydration, avoiding hepatotoxic drugs, and monitoring for complications.
7.1 Pharmacologic Therapy¶
Phenobarbital or rifampin induce UGT1A1 in CN-II. Phototherapy converts bilirubin to water-soluble isomers. Exchange transfusion is critical for CN-I neonates.
7.2 Surgical Interventions¶
Liver transplantation is the definitive treatment for CN-I. Biliary drainage may be required for obstructive cholestasis.
8. PROGNOSIS & COMPLICATIONS¶
GS is benign with no long-term complications. CN-I requires lifelong management to prevent kernicterus. DJS and RS are generally stable but may progress to cirrhosis in rare cases. Severe cholestasis (PFIC) can lead to end-stage liver disease.
8.1 Complications¶
Kernicterus, pruritus, cholangiopathy, and liver failure in severe cases. Drug interactions (e.g., irinotecan) may exacerbate hyperbilirubinemia.
9. SPECIAL CONSIDERATIONS¶
Pregnancy may worsen GS or BRIC. Neonates with hemolysis require close monitoring for kernicterus. Patients with GS may have altered drug metabolism (e.g., irinotecan toxicity).
9.1 Pediatrics¶
Neonatal jaundice requires phototherapy. Breast milk jaundice may resolve spontaneously. Hemolysis in infants can lead to severe unconjugated hyperbilirubinemia.
10. KEY POINTS & CLINICAL PEARLS¶
- Bilirubin metabolism involves uptake, conjugation, and excretion.
- GS is the most common unconjugated hyperbilirubinemia.
- CN-I requires liver transplantation; CN-II responds to phenobarbital.
- DJS and RS are benign with normal liver function.
- Phototherapy is critical for severe unconjugated hyperbilirubinemia.
- Genetic testing confirms diagnosis of inherited disorders.