Jaundice & Hereditary Hyperbilirubinemias
A high-yield Step 1 walkthrough of bilirubin metabolism and jaundice, anchored on the unconjugated-vs-conjugated fork and the five hereditary hyperbilirubinemias (Gilbert, Crigler-Najjar I/II, Dubin-Johnson, Rotor), with vignettes, a next-best-step work-up, and the neonatal jaundice buckets.
Bilirubin metabolism & the jaundice framework
Jaundice (icterus) is yellowing of skin and sclera from bilirubin deposition, clinically visible once total bilirubin > ~2–2.5 mg/dL (scleral icterus is earliest). Heme from senescent RBCs is degraded by heme oxygenase → biliverdin → (biliverdin reductase) → unconjugated bilirubin (UCB) in reticuloendothelial macrophages. UCB is lipophilic, albumin-bound, and water-insoluble — it is NOT excreted in urine but CAN cross the blood–brain barrier (kernicterus in neonates). Hepatocytes take up UCB, and UGT1A1 conjugates it with glucuronic acid → conjugated (direct) bilirubin, which is water-soluble and secreted into bile via MRP2. Gut bacteria then form urobilinogen/stercobilin.
The first fork on boards is unconjugated vs conjugated hyperbilirubinemia. Because only conjugated bilirubin is water-soluble, bilirubinuria (dark urine) implies a conjugated (direct) process; pure hemolysis/unconjugated states produce no urine bilirubin.
- Unconjugated (indirect): overproduction (hemolysis, ineffective erythropoiesis), ↓ uptake, or ↓ conjugation (Gilbert, Crigler-Najjar, physiologic neonatal, breast-milk jaundice).
- Conjugated (direct): ↓ excretion — hepatocellular injury, biliary obstruction, or inherited Dubin-Johnson / Rotor.
- Direct fraction > 20% of total defines conjugated hyperbilirubinemia.
- Urine bilirubin appears only with conjugated (water-soluble) bilirubin; it is absent in hemolysis.
- Urine urobilinogen: ↑ in hemolysis; ↓/absent in complete biliary obstruction (with acholic/pale stools).
- Hemolysis clues: ↑ LDH, ↑ reticulocytes, ↓ haptoglobin, ↑ indirect bilirubin.
- UGT1A1 is the shared conjugating enzyme across the severity spectrum Gilbert → Crigler-Najjar II → Crigler-Najjar I.
The hereditary hyperbilirubinemias
| Syndrome | Bilirubin | Defect | Key clue / severity |
|---|---|---|---|
| Gilbert | Unconjugated | ↓ UGT1A1 activity (~30%); promoter TA-repeat polymorphism | Mild; unmasked by fasting, stress, illness; benign & common |
| Crigler-Najjar I | Unconjugated | Absent UGT1A1 | Severe neonatal; kernicterus, fatal; no response to phenobarbital; needs phototherapy + liver transplant |
| Crigler-Najjar II | Unconjugated | Markedly ↓ UGT1A1 | Milder; responds to phenobarbital (induces residual UGT1A1) |
| Dubin-Johnson | Conjugated | MRP2 (ABCC2) canalicular excretion defect | Benign; grossly black liver; urine coproporphyrin I > 80% (total normal) |
| Rotor | Conjugated | Hepatic uptake/storage (OATP1B1/1B3) | Benign; liver NOT black; total urine coproporphyrin markedly ↑ |
Vignette: A 19-year-old man notices mild scleral yellowing during finals week after skipping meals and pulling all-nighters, shortly following a viral illness. He feels well. Labs: total bilirubin 2.8 mg/dL, indirect 2.4; AST/ALT, alkaline phosphatase, CBC, reticulocyte count, LDH, and haptoglobin all normal; no urine bilirubin.
Diagnosis: Gilbert syndrome — mild unconjugated hyperbilirubinemia unmasked by fasting/stress/illness, with normal LFTs and no hemolysis.
Next best step: Reassurance — it is benign and needs no treatment or further work-up. Do not order a liver biopsy. Isolated indirect hyperbilirubinemia with normal CBC/reticulocytes/haptoglobin effectively excludes hemolysis.
Vignette: A 4-day-old breastfed neonate is deeply jaundiced with total bilirubin 24 mg/dL (mostly indirect), poor feeding, lethargy, and an emerging high-pitched cry with hypertonia and retrocollis; bilirubin was already very high on day 2. Hemolytic disease (ABO/Rh, G6PD) has been excluded.
Diagnosis: Severe unconjugated hyperbilirubinemia → acute bilirubin encephalopathy / kernicterus, with UCB deposition in the basal ganglia (globus pallidus, subthalamic nucleus). Extreme, early, persistent elevation without hemolysis suggests Crigler-Najjar type I (absent UGT1A1).
Next best step: Intensive phototherapy (isomerizes UCB to water-soluble lumirubin) plus exchange transfusion for encephalopathy — indicated regardless of underlying cause at this level with neurologic signs. Type I does not respond to phenobarbital and ultimately needs liver transplant; type II improves with phenobarbital.
- Dubin-Johnson = Dark liver (both start with D). Rotor = Regular-colored liver (not black) — the key gross-pathology distinction between the two benign conjugated syndromes.
- "Conjugated goes into the urine": only conjugated (water-soluble) bilirubin darkens urine; unconjugated stays out of urine (albumin-bound, fat-soluble → crosses the BBB → kernicterus).
- Crigler-Najjar II can be Induced: phenobarbital induces residual UGT1A1 in type II; type I has none, so it does not respond.
- Fractionate bilirubin → unconjugated vs conjugated.
- Isolated unconjugated + normal LFTs → check hemolysis labs (reticulocytes, LDH, haptoglobin, smear). No hemolysis → Gilbert → reassure.
- Conjugated → look at the LFT pattern:
- Hepatocellular (↑↑ AST/ALT) → viral/alcoholic/autoimmune hepatitis work-up.
- Cholestatic/obstructive (↑↑ ALP/GGT, ↑ direct) → RUQ ultrasound first to assess ducts. Dilated ducts → obstruction (stones, tumor).
- Painless jaundice + weight loss + palpable, nontender, enlarged gallbladder (Courvoisier sign) → pancreatic head cancer until proven otherwise.
- Neonate: jaundice in the first 24 h is always pathologic (hemolysis/sepsis); physiologic jaundice peaks day 3–5.
Neonatal jaundice — the four buckets
| Type | Timing | Mechanism | Key point |
|---|---|---|---|
| Physiologic | Onset > 24 h, peaks day 3–5 | Immature UGT1A1 + high RBC turnover | Unconjugated; self-limited |
| Breastfeeding-failure ("not enough") | First week | Poor intake → dehydration, ↓ stooling, ↑ enterohepatic recirculation | Unconjugated; improve feeding |
| Breast-milk jaundice ("too much") | ~Day 7–14, peaks wk 2 | Milk β-glucuronidase deconjugates bilirubin → ↑ enterohepatic recirculation | Unconjugated; benign, continue nursing |
| Pathologic | < 24 h of life | Hemolysis (ABO/Rh), sepsis, G6PD | Always work up; kernicterus risk |
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