Which of the following BEST describes the mechanism by which phototherapy lowers serum bilirubin in a neonate?

• A Induction of hepatic uridine diphosphoglucuronosyltransferase activity
• B Photoisomerisation of unconjugated bilirubin into water-soluble forms excreted without conjugation ✓
• C Enhancement of enterohepatic circulation of bilirubin through the gut
• D Increased dissociation of bilirubin from albumin allowing renal filtration

Explanation

Light in the blue-green spectrum converts toxic unconjugated 4Z,15Z bilirubin into configurational isomers and lumirubin, a structural isomer that is water soluble and excreted in bile and urine without needing hepatic conjugation. Lumirubin formation is irreversible and faster than configurational isomerisation. Phototherapy does not induce glucuronyl transferase, it reduces rather than enhances enterohepatic circulation, and free bilirubin released from albumin would be more dangerous, not less.

Reference: Nelson Textbook of Pediatrics, 21st ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

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