The Effect of Hematin on Bilirubin Binding in Bilirubin-Enriched Neonatal Cord Serum

It has been suggested that the serum of infants with ABO hemolytic disease contains hematin which might interfere with bilirubin binding to albumin, increasing the risk of kerincterus. Using the horseradish peroxidase assay, we investigated this possibility. Cord serum from healthy term infants was enriched with bilirubin to a bilirubin/albumin molar ratio of 0.6, and then varying amounts of hematin were added. Hematin had a significant adverse effect on bilirubin binding when present in half to equimolar ratios with bilirubin. This high concentration of hematin does not appear to be present in serum from infants with ABO hemolytic disease and no difference was seen when comparing the dilute and the undilute peroxidase assays. These data suggest that hematin can alter bilirubin binding in neonatal serum but is not os physiologic importance for infants with ABO-isoimmune hemolysis.