Unbound bilirubin concentration is associated with abnormal automated auditory brainstem response for jaundiced newborns.

OBJECTIVE: This study was conducted to determine whether incidental jaundice affects automated auditory brainstem response results.

METHODS: We reviewed the medical charts of jaundiced newborns of > or = 34 weeks of gestation who underwent automated auditory brainstem response testing within 4 hours of plasma total bilirubin concentration and unbound bilirubin concentration measurements. We tested the hypothesis that the likelihood of abnormal automated auditory brainstem response results would increase as total bilirubin and unbound bilirubin concentrations increased.

RESULTS: Forty-four infants with proximate total bilirubin concentration, unbound bilirubin concentration, and automated auditory brainstem response measurements were identified, and 4 (9%) had bilateral refer automated auditory brainstem response results. The mean total bilirubin concentration of 21.4 mg/dL (SD: 4.0 mg/dL; range: 14.4-29.5 mg/dL) for the 40 infants with bilateral pass automated auditory brainstem response results was not significantly different from that of 23.0 mg/dL (range: 14.9-33.1 mg/dL) for the 4 infants with bilateral refer automated auditory brainstem response results. However, the mean unbound bilirubin concentration of 1.32 microg/dL (range: 0.22-2.99 microg/dL) for the 40 infants with bilateral pass results was significantly lower than the mean of 2.62 microg/dL (range: 0.88-4.41 microg/dL) for the 4 infants with bilateral refer results. Logistic regression showed that increasing unbound bilirubin concentrations but not increasing total bilirubin concentrations were associated with of bilateral refer automated auditory brainstem response results.

CONCLUSIONS: The probability of bilateral refer automated auditory brainstem response results increases significantly with increasing unbound bilirubin concentrations but not with increasing total bilirubin concentrations. Because unbound bilirubin concentrations are also more closely correlated with bilirubin neurotoxicity than are total bilirubin concentrations, bilateral refer automated auditory brainstem response results for jaundiced newborns may indicate increased risk of bilirubin neurotoxicity, in addition to the possibility of congenital deafness.