Jaundice - Short Note

Definition

• Biochemistry, Lippincott Illustrated Reviews, 8th ed., p. 799
• Schwartz's Principles of Surgery, 11th ed., p. 1381

Bilirubin Metabolism (Background)

1. Heme from senescent RBCs is catabolized by macrophages → free bilirubin (unconjugated, lipophilic)
2. Unconjugated bilirubin (UCB) binds albumin in plasma → transported to the liver
3. Hepatocytes conjugate UCB with glucuronic acid via UGT1A1 → water-soluble conjugated bilirubin (CB, "direct bilirubin")
4. CB is secreted into bile canaliculi (rate-limiting, energy-dependent step)
5. In intestine, gut bacteria reduce CB → urobilinogen → stercobilin (brown stool color). Some urobilinogen is reabsorbed → excreted in urine as urobilin (yellow urine color)

Classification

1. Prehepatic (Hemolytic) Jaundice

• Cause: Excessive hemolysis overwhelms the liver's conjugating capacity
• Examples: Sickle cell anemia, G6PD deficiency, pyruvate kinase deficiency, immune hemolytic anemias, malaria
• Biochemistry: Elevated UCB only; CB normal or high-normal; urobilinogen increased in urine; no bilirubin in urine; stools normally colored
• Also includes protein-loss states (burns, malnutrition) - decreased albumin fails to carry UCB to liver

Mechanism of hemolytic (A) and neonatal (B) jaundice - Lippincott Biochemistry, 8th ed.

2. Hepatocellular (Intrahepatic) Jaundice

• Cause: Liver cell damage impairs conjugation and/or excretion
• Examples: Viral hepatitis, cirrhosis, alcoholic liver disease, sepsis, drug toxicity (acetaminophen, oral contraceptives, anabolic steroids), autoimmune hepatitis
• Inherited disorders:
  • Gilbert's syndrome - mild UGT1A1 deficiency (~4-7% of population); benign, mild UCB rises with fasting/stress
  • Crigler-Najjar syndrome - near-complete/complete UGT1A1 deficiency; rare, severe; can cause kernicterus in neonates
  • Dubin-Johnson syndrome / Rotor's syndrome - defects in secretion of CB from hepatocyte into bile → conjugated hyperbilirubinemia
• Biochemistry: Both UCB and CB elevated; ALT/AST elevated; urinary urobilinogen increased; dark urine; pale stools

3. Posthepatic (Obstructive/Extrahepatic Cholestatic) Jaundice

• Cause: Obstruction of the biliary ductal system preventing CB flow into duodenum
• Intrinsic: Cholelithiasis, choledocholithiasis, cholangiocarcinoma, biliary strictures, cholangitis, papilla of Vater disorders, primary sclerosing cholangitis
• Extrinsic: Carcinoma head of pancreas (commonest malignant cause), pancreatitis, pseudocyst
• Iatrogenic: Surgical clips, retained stones, bile duct ischemia
• Biochemistry: Elevated CB (conjugated hyperbilirubinemia); CB appears in urine (dark urine - "cola-colored"); urinary urobilinogen absent; stools pale/clay-colored; GI pain, nausea

Neonatal Jaundice

• Occurs in ~60% of full-term and ~80% of preterm neonates
• Due to: high RBC turnover + immature UGT1A1 (reaches adult levels at ~4 weeks)
• Physiological neonatal jaundice: transient UCB rise in first postnatal week, self-limiting
• Pathological causes: isoimmunization (Rh/ABO), heritable hemolytic disorders, extravasated blood (cephalhematoma), Crigler-Najjar syndrome
• Kernicterus: UCB >20-25 mg/dL (exceeds albumin binding capacity) crosses the blood-brain barrier → deposits in basal ganglia → toxic encephalopathy, hearing loss, choreoathetosis
• Treatment: Blue fluorescent light (phototherapy) converts UCB to water-soluble photoisomers excreted in bile without conjugation; exchange transfusion in severe cases

Lab Findings Summary Table

Bilirubin Measurement

• Direct bilirubin = CB (reacts rapidly in aqueous solution within 1 minute)
• Total bilirubin = reaction in methanol (both CB + UCB)
• Indirect bilirubin = Total minus Direct = UCB

Key Clinical Approach (Workup)

1. History: Drug history, alcohol use, viral exposure, family history, pain (obstructive causes often painful), weight loss
2. Examination: Scleral icterus (first sign), hepatomegaly, splenomegaly, stigmata of chronic liver disease, Courvoisier's sign (palpable non-tender gallbladder in malignant obstruction)
3. Labs: LFTs (bilirubin, ALT, AST, ALP, GGT), albumin, PT/INR, CBC, peripheral smear, viral hepatitis markers, urine bilirubin & urobilinogen
4. Imaging: Ultrasound (first-line to detect ductal dilatation), CT/MRCP (for extent and cause), ERCP (therapeutic)

Sources

• Biochemistry, Lippincott Illustrated Reviews, 8th ed., pp. 798-805
• Schwartz's Principles of Surgery, 11th ed., pp. 1381-1382
• Medical Physiology (Boron & Boulpaep), Chapter 46
• Goldman-Cecil Medicine, International Edition

Classification and Causes of Jaundice

I. Classification Based on Bilirubin Type

• Harper's Illustrated Biochemistry, 32nd ed.

II. Physiological (Anatomical) Classification

A. PREHEPATIC JAUNDICE (Unconjugated Hyperbilirubinemia)

1. Increased Production of UCB from Heme

• Hereditary spherocytosis
• G6PD deficiency
• Pyruvate kinase deficiency
• Sickle cell anemia
• Thalassemia

• Immune-mediated: autoimmune hemolytic anemia, transfusion reactions, drugs (methyldopa, penicillin) - Coombs positive
• Non-immune: microangiopathic hemolytic anemia (TTP, HUS, DIC), prosthetic heart valves, infections (malaria, Clostridium), drugs/toxins directly damaging RBCs - Coombs negative

• Megaloblastic anemia (B12/folate deficiency)
• Sideroblastic anemia
• Thalassemia (intramedullary destruction)

2. Decreased Delivery of UCB to Hepatocyte

• Right-sided congestive heart failure
• Portocaval shunt

3. Decreased Uptake of UCB by Hepatocytes

• Competitive inhibition by drugs (rifampicin, flavaspidic acid)
• Gilbert's syndrome (mildly impaired uptake + conjugation)
• Sepsis, fasting

4. Decreased Storage in Cytosol (Reduced Ligandin/Y and Z proteins)

• Competitive inhibition
• Fever

B. HEPATIC (INTRAHEPATIC) JAUNDICE

1. Decreased Conjugation (Unconjugated Hyperbilirubinemia)

2. Defective Secretion of CB into Bile Canaliculi (Conjugated Hyperbilirubinemia)

3. Hepatocellular Disease (Mixed - Cholestatic + Conjugation Defect)

• Hepatitis A, B, C, D, E
• Epstein-Barr virus (EBV/infectious mononucleosis)
• Cytomegalovirus (CMV)
• Herpes simplex virus (HSV)

• Dose-dependent (predictable): acetaminophen, alcohol
• Idiosyncratic (unpredictable): isoniazid, halothane, chlorpromazine
• Environmental toxins: vinyl chloride, pyrrolizidine alkaloids (Jamaica bush tea), wild mushrooms

• Wilson's disease (copper accumulation - young adults)
• Hemochromatosis (iron overload)
• Alpha-1 antitrypsin deficiency
• Non-alcoholic fatty liver disease (NAFLD/NASH)

• Acute fatty liver of pregnancy
• Intrahepatic cholestasis of pregnancy
• HELLP syndrome (hemolysis, elevated liver enzymes, low platelets)

C. POSTHEPATIC (EXTRAHEPATIC OBSTRUCTIVE) JAUNDICE (Conjugated Hyperbilirubinemia)

1. Intraluminal (within the duct)

• Choledocholithiasis (common bile duct stones) - most common benign cause
• Parasites (Ascaris, liver flukes - Clonorchis, Fasciola)
• Blood clots (hemobilia)

2. Mural (wall of the duct)

• Malignant:
  • Cholangiocarcinoma (Klatskin tumor at hilum)
  • Carcinoma of ampulla of Vater
  • Carcinoma of gallbladder
• Benign:
  • Primary sclerosing cholangitis (PSC)
  • Benign biliary strictures (post-surgical, post-traumatic)
  • Biliary atresia (neonates)
  • Cholangitis (bacterial infection of bile duct)
  • Disorders of the papilla of Vater

3. Extrinsic Compression

• Pancreatic carcinoma (head of pancreas) - most common malignant cause of obstructive jaundice
• Chronic pancreatitis / pancreatitis / pseudocysts
• Lymph node enlargement in porta hepatis (lymphoma, metastatic nodes)
• Mirizzi syndrome (gallstone in cystic duct compressing common hepatic duct)

4. Iatrogenic / Post-Surgical

• Accidental bile duct ligation or clipping
• Bile duct ischemia
• Retained stones post-cholecystectomy
• Post-anastomotic strictures

III. Classification Based on Age Group

Neonatal Causes

IV. Quick Causes Summary by Bilirubin Type

• Hemolytic anemias (hereditary + acquired)
• Ineffective erythropoiesis
• Neonatal jaundice
• Gilbert's syndrome
• Crigler-Najjar Types I and II
• Toxic hyperbilirubinemia

• Obstruction of biliary tree (stones, carcinoma, strictures)
• Dubin-Johnson syndrome
• Rotor syndrome
• Liver diseases (hepatitis, cirrhosis, cholestasis)