Serum unbound bilirubin as a predictor for clinical kernicterus in extremely low birth weight infants at a late age in the neonatal intensive care unit.

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This study aimed to evaluate peak serum total bilirubin (TB) and unbound bilirubin (UB) levels in preterm infants with clinical kernicterus (KI) who were diagnosed by clinical findings during infancy. For this multicenter retrospective study, 18 Japanese extremely low birth weight (ELBW) infants with clinical KI were included. Clinical KI was diagnosed based on the presence of motor developmental impairment with/without athetosis, and abnormal magnetic resonance imaging or brainstem auditory evoked potential findings during infancy. High and low TB or UB levels were defined as serum TB levels ⩾ and <15 mg/dL or serum UB levels ⩾ and <0.8 μg/dL, respectively. The clinical characteristics of KI preterm infants were analyzed. The proportion of infants with high or low serum TB levels and with high or low serum UB levels was then investigated. Sensitivity and specificity were calculated. In 18 KI infants, the median age when serum TB levels peaked was 28 days after birth. In eight KI infants with low serum TB levels, 88% of them had high serum UB levels. For comparison of the number of infants who had high or low serum TB and UB levels, the sensitivity was 90% and specificity was 13%. Serum TB and UB levels peak at a later age than expected. Chronic serum UB monitoring may be helpful for identifying ELBW infants at risk for developing KI, even when they do not have high serum TB levels.