Urinary excretion of an isomer of bilirubin during phototherapy.

Lumirubin, a water-soluble photoproduct of bilirubin formed in vivo during phototherapy, is excreted in the urine. In premature infants with little or no bilirubin conjugating activity, lumirubin is the principal yellow pigment found in the urine during phototherapy. The clearance rate of lumirubin in nine premature infants varied from 0.05 to 0.65 ml/min and increased with postconceptional age in parallel with increased creatinine clearance rate. The amount of lumirubin excreted per 24 h was estimated to be from 0.2 to 9.4 mg with a mean of 3.2 mg. The urinary excretion of lumirubin is a significant pathway for pigment elimination during phototherapy.