Demonstration of a geometric isomer of bilirubin-IX alpha in the serum of a hyperbilirubinaemic newborn infant and the mechanism of jaundice phototherapy.

Photobilirubin-IX alpha in the serum of a hyperbilirubinaemic newborn infant was demonstrated for the first time by reversed-phase high-pressure liquid chromatography. The concentrations increased significantly during phototherapy. Corresponding to these changes in the serum, biliary unconjugated bilirubin concentrations increased markedly but photobilirubin-IX alpha was not detected in the bile. Moreover, large amounts of 'unknown pigment' that are diazo-negative appeared in the bile during phototherapy.