INFLUENCE OF PHOTOISOMERS IN BILIRUBIN DETERMINATIONS ON KODAK-EKTACHEM AND HITACHI ANALYZERS IN NEONATAL SPECIMENS - STUDY OF THE CONTRIBUTION OF STRUCTURAL AND CONFIGURATIONAL ISOMERS

We compared data obtained with the Kodak Ektachem and Hitachi 717 Anal ysers and HPLC from 83 neonates cinder phototherapy. Total bilirubin v alues determined with the Kodak and Hitachi are in good agreement, but we observed a large discrepancy in the results for conjugated (Kodak) and direct (Hitachi) bilirubin. HPLC revealed that all the samples co ntained configurational isomers, while only 7.7% and 30.8% contained c onjugated bilirubin and structural isomers, respectively. We developed a device for the specific and quantitative production of configuratio nal or structural isomers, by irradiation with blue or green light. In vitro, total bilirubin values are coherent for the routine analysers in the presence of configurational or structural isomers. With configu rational isomers, unconjugated biliribin (Kodak) is lower than total b ilirubin (Kodak), and conjugated bilirubin (Kodak) is always equal to zero, so the apparatus gives a false positive response for delta bilir ubin. In contrast, the direct bilirubin (Hitachi) is constant. Further more, in the presence of structural isomers, unconjugated bilirubin (K odak) is unexpectedly higher than total bilirubin (Kodak), conjugated bilirubin (Kodak) is proportional to the quantity of these isomers, an d direct bilirubin (Hitachi) is constant. The contribution of photoiso mers in bilirubin measurements is discussed.