A 2-day-old term neonate develops jaundice. Serum total bilirubin is 8.5 mg/dL (145 micromol/L), primarily unconjugated. The infant is breastfeeding well, passing normal stools, and examination shows no hepatosplenomegaly or pallor. Blood group is O positive and mother is O positive with negative Coombs test. What is the diagnosis?

Answer and explanation

Correct answer: A. Physiological neonatal jaundice

  1. Step 1: Physiological jaundice appears after 24 hours of life, peaks at days 3 to 5 (bilirubin < 12-15 mg/dL), and resolves by 1 to 2 weeks.
  2. Step 2: It is caused by transient immaturity of hepatic uridine diphosphate glucuronosyltransferase (UGT1A1) and increased red cell turnover.
Answer
Physiological neonatal jaundice.
Why not the others: 'ABO hemolytic disease of the newborn' typically causes jaundice within the first 24 hours of life with mother O and infant A or B, and a positive Coombs test; 'Biliary atresia' presents in weeks 2 to 6 with conjugated (direct) hyperbilirubinemia and acholic pale stools; 'G6PD deficiency crisis' produces rapid acute intravascular hemolysis.

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