Neonatal Hyperbilirubinemia - Complete Viva Q&A for Final Year MBBS

EASY LEVEL QUESTIONS

Q1. Define neonatal jaundice / hyperbilirubinemia.

Q2. How is bilirubin formed and metabolized?

1. Formation: ~80% from breakdown of hemoglobin (RBC senescence), rest from myoglobin and other heme proteins. Heme → biliverdin (by heme oxygenase) → unconjugated bilirubin (by biliverdin reductase)
2. Transport: Unconjugated bilirubin is water-insoluble and binds to albumin in serum
3. Hepatic uptake: Taken up by hepatocytes via OATP (ligandin/Y protein)
4. Conjugation: UDP-glucuronosyltransferase (UGT1A1) conjugates it to bilirubin diglucuronide (water-soluble)
5. Excretion: Into bile → intestine; gut bacteria convert it to urobilinogen → urobilin (excreted in urine/stool); some urobilinogen reabsorbed (enterohepatic circulation)

Q3. What is physiologic jaundice? When does it appear and resolve?

• Appears in ~50% of normal term newborns
• Timing: Appears after 24 hours of birth; peaks between day 2-5; resolves by end of week 1-2 in term infants; up to 3 weeks in preterm
• Bilirubin level: Usually does not exceed 12-15 mg/dL in term infants
• Three contributing mechanisms:
  1. Increased bilirubin production (fetal RBCs have shorter lifespan ~70-90 days)
  2. Decreased hepatic clearance (immature UGT1A1)
  3. Increased enterohepatic resorption
• Key rule: Jaundice in the FIRST 24 hours is NEVER physiologic - always pathologic

Q4. What is breast milk jaundice? How does it differ from "breastfeeding jaundice"?

Q5. What are the risk factors for severe neonatal hyperbilirubinemia?

• Prematurity (especially <38 weeks - sixfold increase at 36-37 weeks)
• Isoimmune hemolysis - ABO incompatibility, Rh incompatibility
• G6PD deficiency
• Sepsis / infection
• Cephalhematoma or other birth trauma causing extravascular blood resorption
• Dehydration
• Hereditary spherocytosis
• Infant of a diabetic mother (polycythemia)
• East Asian or Mediterranean ethnicity
• Previous sibling requiring phototherapy

Q6. What is kernicterus? What are its clinical features?

• Poor feeding, lethargy, hypotonia/hypertonia
• High-pitched cry
• Fever, irritability

• Opisthotonos (backward trunk arching), retrocollis (neck arching backward)
• Seizures
• Death

• Choreoathetoid cerebral palsy
• Sensorineural hearing loss
• Upward gaze palsy
• Intellectual disability

Q7. What investigations are done in neonatal jaundice?

• Transcutaneous bilirubinometry - quick screening (valid after 24 hrs, before 7 days)
• Total and fractionated (direct/indirect) serum bilirubin - gold standard
• Blood group and Rh type - mother and baby
• Direct Coombs test (DAT) - detects isoimmune hemolysis
• CBC with peripheral smear - polycythemia, spherocytes, hemolysis
• Reticulocyte count - elevated in hemolysis
• G6PD level - in high-risk populations
• Sepsis workup (if sick-appearing): blood culture, CRP, CBC
• Urine for reducing substances - galactosemia
• Thyroid function - hypothyroidism
• Ultrasound abdomen - if conjugated hyperbilirubinemia (biliary atresia workup)
• HIDA scan / liver biopsy - for biliary atresia

Q8. What are the indications for evaluation in a jaundiced neonate?

• Jaundice appearing within first 24 hours of birth
• Elevated direct (conjugated) bilirubin (always pathologic)
• Rapidly rising total serum bilirubin unexplained by history/exam
• Total serum bilirubin approaching exchange transfusion level or not responding to phototherapy
• Jaundice persisting beyond 3 weeks of age
• Sick-appearing infant

Q9. What is the treatment of neonatal hyperbilirubinemia?

• Mechanism: Blue light (wavelength 430-490 nm) converts unconjugated bilirubin in the skin to water-soluble photoisomers (lumirubin, configurational isomers) excreted in bile/urine WITHOUT glucuronidation
• Indications: Based on hour-specific bilirubin nomogram (Bhutani nomogram); generally started at ~15-18 mg/dL in term infants depending on risk factors
• Side effects: Loose stools, rash, "bronze baby syndrome" (in conjugated hyperbilirubinemia), hyperthermia, dehydration

• Indicated when bilirubin is at exchange level (generally >25 mg/dL in term infants, lower thresholds in preterm/sick)
• Removes sensitized RBCs, bilirubin, and antibodies
• Replaces ~85% of circulating blood volume

• For isoimmune hemolytic disease (ABO/Rh incompatibility) if bilirubin rising despite phototherapy
• Reduces hemolysis by blocking Fc receptors on macrophages

• Ensure adequate hydration and nutrition
• Treat underlying cause (sepsis, hypothyroidism, etc.)

HARD LEVEL QUESTIONS

Q10. Explain the pathophysiology of why unconjugated bilirubin is neurotoxic.

1. Free (unbound) bilirubin - the non-albumin-bound fraction - crosses the blood-brain barrier. At very high levels or when albumin binding capacity is saturated, free bilirubin increases.
2. BBB permeability increases in states of acidosis, prematurity, sepsis, and hyperosmolarity, allowing bilirubin entry even at lower levels
3. Bilirubin deposits in the basal ganglia, subthalamic nuclei, globus pallidus, and brainstem nuclei
4. At the cellular level: bilirubin inhibits mitochondrial function, induces oxidative stress, disrupts neuronal membrane function, and promotes apoptosis
5. Albumin binding is reduced by: acidosis (reduces affinity), drugs (sulfonamides, ceftriaxone), free fatty acids (from breast milk, lipid infusions), and hypoalbuminemia (prematurity)

Q11. What is the Bhutani nomogram and why is it used?

• Low risk zone (below 40th percentile)
• Low-intermediate risk zone (40th-75th percentile)
• High-intermediate risk zone (75th-95th percentile)
• High risk zone (above 95th percentile)

Q12. What are the hereditary disorders of bilirubin metabolism? Differentiate them.

Q13. What is ABO incompatibility? How does it differ from Rh incompatibility?

Q14. What are causes of conjugated (direct) hyperbilirubinemia in neonates and how do you approach it?

• Biliary atresia - most important (needs Kasai portoenterostomy before 60 days of age)
• Choledochal cyst
• Neonatal hepatitis (idiopathic, TORCH infections - CMV, toxoplasmosis, rubella, herpes, syphilis)
• Inspissated bile syndrome (after hemolysis)
• Metabolic disorders: galactosemia (urine reducing substances +ve), tyrosinemia, alpha-1 antitrypsin deficiency, hypothyroidism, cystic fibrosis
• Alagille syndrome (paucity of intrahepatic bile ducts)
• TPN-associated cholestasis in preterm infants
• Sepsis / UTI

1. Confirm conjugated hyperbilirubinemia
2. LFTs, GGT (markedly elevated in biliary atresia), coagulation
3. Urine for reducing substances (galactosemia), metabolic screen
4. TORCH serology
5. Abdominal ultrasound
6. HIDA scan - no excretion into bowel suggests biliary atresia
7. Liver biopsy if needed
8. Kasai procedure (hepatic portoenterostomy) for biliary atresia - best done before 60 days

Q15. What is "bronze baby syndrome"? When does it occur?

Q16. What is the "free bilirubin" concept? What drugs displace bilirubin from albumin?

• Ceftriaxone (displaces bilirubin - contraindicated in neonates, especially jaundiced ones)
• Sulfonamides / sulfisoxazole
• Salicylates
• Furosemide (high doses)
• Free fatty acids (compete for albumin binding)

• Hypoalbuminemia (prematurity)
• Acidosis (reduces affinity of albumin for bilirubin)
• Elevated free fatty acids

Q17. Describe the mechanism of phototherapy in detail.

1. Configurational isomerization (fastest): Unconjugated bilirubin 4Z,15Z isomer → 4E,15Z or 4Z,15E isomers (less lipophilic, can be excreted in bile without conjugation) - rapidly reversible
2. Structural isomerization (lumirubin) (most important): 4Z,15Z bilirubin → lumirubin (irreversible ring structure, rapidly excreted in bile) - accounts for most bilirubin clearance
3. Photo-oxidation (slowest): Bilirubin oxidized to colorless polar compounds excreted in urine

• Effective phototherapy requires maximum skin exposure (undress baby, eye protection, gonads covered)
• "Intensive phototherapy" = irradiance >30 µW/cm²/nm with special blue lights
• Fiberoptic ("bili-blanket") phototherapy allows continued feeding
• Efficacy decreases as bilirubin rises (fewer skin receptors become occupied with photoproducts)

Q18. What are the indications and steps for exchange transfusion?

• Total serum bilirubin reaching exchange level despite intensive phototherapy (per AAP nomogram, generally >25 mg/dL in term infants, lower for preterm)
• Signs of acute bilirubin encephalopathy (ABE) at any bilirubin level
• Severe isoimmune hemolytic disease with rapid rise not responding to phototherapy + IVIG

• Volume = 2 × 85 mL/kg (= ~160-170 mL/kg total) - removes ~85% of circulating RBCs
• Blood used: Fresh whole blood or reconstituted (PRBC + FFP) matched to baby's blood type and crossmatched against mother's serum; irradiated and CMV-negative
• Route: Umbilical venous catheter (most common) - push-pull technique
• Aliquots: 5-20 mL per exchange depending on baby's weight

Q19. What is the AAP 2022 update on neonatal hyperbilirubinemia management?

1. Gestational-age-specific thresholds - separate phototherapy and exchange thresholds for infants 35-37 weeks, 38-39 weeks, and ≥40 weeks
2. Lower thresholds for infants with neurotoxicity risk factors (isoimmune hemolysis, G6PD deficiency, albumin <3.0 g/dL, sepsis, respiratory acidosis)
3. Universal pre-discharge bilirubin screening (TSB or TcB) with hour-specific assessment
4. Outpatient phototherapy can be considered for low-risk infants with mild-moderate elevation
5. Discontinue phototherapy when bilirubin is 2 mg/dL below threshold; rebound check after 24 hrs
6. IVIG recommended (0.5-1 g/kg) for isoimmune hemolytic disease with rapidly rising bilirubin despite phototherapy

Q20. (Classic hard viva) A 3-day-old term baby presents with jaundice. TSB = 22 mg/dL. The baby looks lethargic, poor feeder, has a high-pitched cry. What do you do?

1. Admit to NICU - do NOT discharge
2. Start intensive phototherapy immediately (naked, maximum skin exposure, special blue lights, >30 µW/cm²/nm irradiance)
3. Urgent investigations:
   • Repeat TSB every 2-4 hours
   • Blood group and Rh (mother and baby)
   • Direct Coombs test
   • CBC, peripheral smear, reticulocyte count
   • Serum albumin, electrolytes, blood glucose
   • Blood culture (rule out sepsis)
4. Prepare for exchange transfusion - at 22 mg/dL with ABE signs, exchange transfusion is indicated regardless of bilirubin level alone
5. IVIG (0.5-1 g/kg IV) if Coombs positive
6. IV fluids if dehydrated; ensure adequate nutrition
7. Parental counseling about ABE and prognosis
8. Neurology / audiology follow-up (BAER/BERA for sensorineural hearing loss)

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