Bilirubin-IX beta is a marker of meconium, like zinc coproporphyrin

Background: Because meconium accumulates continuously in the fetal intestin e, analysis of the postnatally excreted material could yield important info rmation of intrauterine metabolism and maturation. Therefore, a study of th e bilirubin pigments in meconium and in the first neonatal stools was carri ed out. Methods: Meconium and stools from 37 neonates of various gestational ages w ere collected carefully, and stored at -20 degreesC, protected by aluminium foil. Samples were defrosted, vortex mixed with an equal amount of dimethy l sulfoxide, centrifuged, and submitted to analysis by high-pressure liquid chromatography using newly developed methods to identify and to quantitate the bilirubin-IX alpha, -IX beta, -IX gamma, and -IX delta isomers. In add ition, samples were also submitted to diazo coupling with ethyl anthranilat e. Total coproporphyrins and zinc coproporphyrin were assayed for compariso n. Results: Unconjugated bilirubin-IX alpha and -IX beta were detected in meco nium but not the -IX gamma or the -IX delta isomer. Bilirubin-IX beta was t he predominant pigment and comprised 63% to 96% of the unconjugated bilirub ins in the first sample of meconium excreted. Its amount decreased rapidly during the first 5 days in full-term newborns, but this occurred more slowl y in preterm neonates, especially in those with a gestational age less than 30 weeks. The decrease of bilirubin-IX beta over time correlated with that of coproporphyrin. Conclusions: Bilirubin-IX beta is the prevailing bile pigment in the first excreted sample of meconium. It gradually decreases after birth and can be considered a biochemical marker of meconium, like zinc coproporphyrin.