Phototherapy is used when bilirubin reaches what threshold?

• A. When bilirubin is undetectable.
• B. At any bilirubin level.
• C. Phototherapy is never used.
• D. When bilirubin reaches treatment thresholds.

Answer: (D)

Phototherapy is started when bilirubin reaches treatment thresholds because those thresholds are the trigger point at which the risk of bilirubin-related neurotoxicity becomes significant and intervention is warranted. Bilirubin levels rise after birth, and the decision to initiate therapy isn’t at any level or only when undetectable; it’s based on guideline-defined thresholds that vary with how old the infant is (in hours) and their gestational age, along with other risk factors. Phototherapy works by converting bilirubin into water-soluble photoisomers that are excreted without needing further liver processing, so starting therapy at the threshold helps prevent potential complications like kernicterus.