Which is a common cause of falsely elevated bilirubin in newborns requiring careful interpretation?

• A. Physiologic jaundice due to immature hepatic conjugation pathways
• B. Breast milk jaundice due to enzyme activity
• C. Hemolytic disease of the newborn
• D. Inherited conjugation defect

Answer: (A)

Bilirubin metabolism in newborns is shaped by the maturity of the liver’s ability to conjugate. In the liver, bilirubin (unconjugated and fat-soluble) must be converted by the enzyme UDP-glucuronosyltransferase to become water-soluble for excretion. At birth, this conjugation system is immature, especially in preterm infants, so unconjugated bilirubin can accumulate. This physiologic jaundice is very common and reflects normal developmental physiology rather than disease, which is why it often requires careful interpretation: clinicians monitor bilirubin levels in the context of the infant’s age in hours and gestational age to decide if it’s rising within expected physiologic limits or signaling a more serious problem.

Other causes described are real conditions but are not as common in healthy newborns or don’t fit the typical early-postnatal pattern. Breast milk–related jaundice usually appears later and is linked to factors in the milk that affect bilirubin processing or reabsorption. Hemolytic disease of the newborn causes rapid, often severe elevations with accompanying anemia and signs of alloimmune destruction. Inherited conjugation defects are rare and usually present differently, not as the typical early physiologic pattern.