A term neonate develops jaundice on day 2 of life with indirect bilirubin 14 mg/dL. Which physiological mechanism is PRIMARILY responsible for physiological jaundice of the newborn?

• A Immune-mediated hemolysis from residual maternal antibodies crossing placenta
• B Combination of increased bilirubin load from HbF breakdown and immature hepatic UDP-glucuronyl transferase activity ✓
• C Decreased albumin synthesis impairing bilirubin transport to the liver
• D Biliary atresia causing conjugated hyperbilirubinemia in the immediate newborn period

Explanation

Physiological jaundice of the newborn results from two concurrent phenomena: (1) increased bilirubin production — HbF has a shorter RBC lifespan (~70-90 days vs. adult 120 days), and the neonatal RBC mass is high; (2) hepatic immaturity — UDP-glucuronyl transferase activity is low at birth, reducing the liver's conjugation capacity. This leads to unconjugated hyperbilirubinemia peaking on days 2-4. Option A describes hemolytic disease of newborn (not physiological); option C is minor; option D would present as conjugated (direct) hyperbilirubinemia and not on day 2.

Reference: Guyton & Hall, Textbook of Medical Physiology, 14th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

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