UNCONJUGATED AND CONJUGATED BILIRUBIN PIGMENTS DURING PERINATAL-DEVELOPMENT V - EFFECT OF PHOTOTHERAPY ON SERUM CONJUGATED BILIRUBIN IN HYPERBILIRUBINEMIC NEONATES

Objective: To determine the effect of phototherapy on serum conjugated bilirubin fractions, an index of bilirubin conjugation, in hyperbilir ubinemic neonates. Method: Serum was sampled from 21 jaundiced (serum diazo total bilirubin greater than or equal to 274 mu mol/l), term, ot herwise healthy neonates prior to starting phototherapy,and 24 h after the commencement of treatment. Alkaline methanolysis followed by reve rse-phase, high-performance liquid chromatography, specific for determ ination of unconjugated bilirubin and the monoconjugated and diconjuga ted fractions of total conjugated bilirubin in serum, was used for the analysis. Prephototherapy values were compared to those at 24 h. Resu lts: Serum total bilirubin and total conjugated bilirubin values decre ased during the study period, from 220 (211-239) to 177 (157-213) mu m ol/l (median (25-75% range))p = 0.001, for the former, and from 1.4 (0 .87-1.57) to 0.93 (0.69-1.84) mu mol/l, p = 0.005, for the latter. The se parameters decreased by a similar percentage (-16.6 +/- 14.8% and - 14.0 +/- 23.4%, respectively; p > 0.05). Both monoconjugated and dicon jugated bilirubin, calculated as a percentage of total conjugated bili rubin, remained constant over the study period (88.2 (72.2-96.4)% befo re phototherapy and 92.5 (87.3-96.8)% after 24 h, p > 0.05, for monoco njugated bilirubin, and 11.8 (3.6-27.8)% and 7.5 (3.2-12.7)%, respecti vely, p > 0.05, for diconjugated bilirubin). Conclusions: Serum total conjugated bilirubin values decreased in parallel to serum total bilir ubin levels during phototherapy, maintaining a constant relationship b etween these two parameters. The ratios of monoconjugated and diconjug ated bilirubin to total conjugated bilirubin remained constant. These findings imply that phototherapy does not alter bilirubin conjugation in hyperbilirubinemic neonates.