Determination of serum unbound bilirubin for prediction of kernicterus in low birthweight infants.

Serum unbound bilirubin concentrations (UBC) and serum total bilirubin concentrations (TBC) were measured serially in 138 low birthweight (LBW) infants treated with phototherapy for non-hemolytic hyperbilirubinemia. We attempted to assign the suitable critical UBC levels for predicting bilirubin encephalopathy into two different birthweight groups: a very low birthweight (VLBW) group (birthweight < 1,500 g) and an LBW group (birthweight between 1,500 g and 2,499 g). Twelve infants were diagnosed as 'at risk' for kernicterus, of whom 11 had signs of acute bilirubin encephalopathy and received exchange transfusion. One VLBW infant had neurological sequelae at a 3 year follow-up, although exchange transfusion was not carried out because of low TBC. Sensitivity and specificity for predicting kernicterus were calculated at different UBC levels between 0.6 microgram/dl and 1.5 micrograms/dl and TBC levels between 8 mg/dl and 26 mg/dl. The receiver-operating characteristic (ROC) curves plotted for UBC as a predictor of kernicterus were clearly shifted up and to the left compared with the curves for TBC in the VLBW and LBW groups. Thus, the UBC measurement may well provide a more rational basis for evaluating the risk of kernicterus in LBW infants. The optimal cut-off points were derived from these curves. In the VLBW group, the sensitivity was 100% and the specificity was 96% for a UBC of 0.8 microgram/dl, and 80% and 64% for a TBC of 11 mg/dl. In the LBW group, the sensitivity was 100% and the specificity was 98% for a UBC of 1.0 microgram/dl and 71% and 78% for a TBC of 16 mg/dl.(ABSTRACT TRUNCATED AT 250 WORDS)