Bilirubin‐IXβ Is a Marker of Meconium, Like Zinc Coproporphyrin

Abstract

BackgroundBecause meconium accumulates continuously in the fetal intestine, analysis of the postnatally excreted material could yield important information of intrauterine metabolism and maturation. Therefore, a study of the bilirubin pigments in meconium and in the first neonatal stools was carried out.MethodsMeconium and stools from 37 neonates of various gestational ages were collected carefully, and stored at −20°C, protected by aluminium foil. Samples were defrosted, vortex mixed with an equal amount of dimethyl sulfoxide, centrifuged, and submitted to analysis by high‐pressure liquid chromatography using newly developed methods to identify and to quantitate the bilirubin‐IXα, ‐IXβ, ‐IXγ, and ‐IXδ isomers. In addition, samples were also submitted to diazo coupling with ethyl anthranilate. Total coproporphyrins and zinc coproporphyrin were assayed for comparison.ResultsUnconjugated bilirubin‐IXα and ‐IXβ were detected in meconium but not the ‐IXγ or the ‐IXδ isomer. Bilirubin‐IXβ was the predominant pigment and comprised 63% to 96% of the unconjugated bilirubins in the first sample of meconium excreted. Its amount decreased rapidly during the first 5 days in full‐term newborns, but this occurred more slowly in preterm neonates, especially in those with a gestational age less than 30 weeks. The decrease of bilirubin‐IXβ over time correlated with that of coproporphyrin.ConclusionsBilirubin‐IXβ 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.