Objectives: To investigate whether serum total bilirubin concentration (TBC) and unbound bilirubin concentration (UBC) reflect the neurological signs such as consciousness, muscle tone, crying and brainstem auditory evoked potentials (BAER) in hyperbilirubinemic infants.

Methods and Materials: The study population consists of 184 hyperbilirubinemic infants with TBC ≥ 18 mg/dl admitted to NICUs between January 1994 and December 1995, including 17 hemolytic diseases, 34 enclosed hemorrhage and 8 infectious diseases. All infants were born with gestation≥ 36 weeks and birth weight ≥ 2500 g, and excluded CNS anomalies. Abnormal neurological signs were evaluated by BIND score more than one and/or abnormalities of BAER based on peak latencies of I, III, V waves and the amplitude. Serum TBC and UBC were determined using UB analyzer (Arrows Co, Osaka).

Results: Of 184 infants, 28 infants showed abnormal neurological signs. TBC levels ≥ 22.0 mg/dl detected abnormal neurological signs with 54% sensitivity and 80% specificity, and UBC levels ≥ 1.0 μg/dl with 71% sensitivity and 77% specificity. Odd's ratios to detect abnormal neurological signs were 6.0 at UBC levls ≥ 1.0 μg/dl (p<0.001), 2.6 at TBC levels≥22 mg/dl (p=0.052), 2.3 for hemolytic diseases, and 1.3 for infectious diseases by logisitic regression analysis.

Conclusions: UBC determination is correlatd with, and highly predictive of, abnormal neurological signs in hyperbilirubinemic infants.