A prospective study of free bilirubin and other risk factors in the development of kernicterus in premature infants.

To assess the value of free bilirubin (FB) measurements in predicting kernicterus (KI) in sick premature infants, 91 newborns weighing less than 1,500 gm at birth were observed during the first week of like with twice daily FB and total bilirubin determinations. Autopsies were performed on 30 of the 53 infants who died. Seven had KI and 23 did not. There were no differences between infants with and with out KI in the maximum FB level (KI 18.2 +/- 4.5 [SEM] nm/liter, no KI 11.1 +/- 0.9 nm/liter, P not significant) or the total bilirubin level (KI 7.3 +/- 1.3 mg/100 ml, no KI 6.1 +/- 0.5 mg/100 ml, P not significant). In fact, three kernicteric infants had very low maximum FB levels (less than 10 nm/liter). These three infants had prolonged episodes of acidosis, hypoxemia, or hypothermia during the 24 hours preceding their maximum level of FB. Although elevated levels of FB may be predictive of KI in some infants, other factors may make the blood-brain barrier more permeable to low levels of FB. This may limit the clinical applicability of FB measurements.