Serum Bilirubin Mono- and Diconjugates in Human Newborns
Several alterations of bilirubin metabolism are present during the neonatal period, all essentially leading to an increased load of unconjugated bilirubin and a decreased hepatic handling of the pigment. The resulting neonatal jaundice is a classical example of unconjugated hyperbilirubinemia(1). The presence of conjugated bilirubin in neonatal plasma has often been investigated, and considered as an index of function of hepatic conjugation or secretion(2–5). Unfortunately, several methodological problems are met when trying to measure serum conjugated bilirubin in the presence of high concentrations of the unconjugated pigment. Most procedures for measurement of bilirubins in biological samples rely on diazo-cleavage, resulting in splitting of the tetrapyrrole moiety and producing dipyrrolic red azoderivatives. After the discovery that bilirubin in bile reacts rapidly, without requiring the presence of an “accelerator”, the distinction between direct-reacting and total bilirubin was introduced. However, “direct-reacting” bilirubin is just operationally defined, and it is therefore dependent on reaction conditions and sample composition, while it does not accurately reflect conjugated bilirubin(6). The ethyl-anthranilate method is more specific, and allows to separate and identify the dipyrrole azoderivatives(6). However, it is impossible to relate the sugar-conjugated azodipyrroles to the parent rubins. A similar problem is present with the isotope-dilution method(2). Direct analysis of the tetrapyrroles has been tried by various solvent-partition and chromatographic procedures, but none of these methods proved to be truly specific and accurate(6).
KeywordsHigh Performance Liquid Chromatography Bile Acid Total Bile Acid Serum Bile Acid Neonatal Jaundice
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