Bilirubin Albumin Binding and Unbound Unconjugated Hyperbilirubinemia in Premature Infants.

Objective: To evaluate the associations between unbound bilirubin (UB) and total serum bilirubin (TSB), bilirubin:albumin molar ratio (BAMR), and bilirubin albumin binding affinity (Ka) as a function of gestational age (GA) in infants born at 24-33 weeks GA.

Study Design: In a prospective observational study, TSB and UB were measured twice daily at least 8 hours apart during the first postnatal week. Serum albumin was measured to calculate BAMR on each day. The highest UB on each day, corresponding TSB, and serum albumin were used to calculate the Ka on each day.

Results: For the 166 infants studied, peak UB significantly correlated with concomitant Ka (r = -0.44, P = .001) but not with concomitant TSB or BAMR after adjusting for GA. On multiple regression analyses, there was a significant association of concomitant Ka (-0.06, 95% CI -0.08 to -0.04, P = .0001), but not concomitant TSB or BAMR with peak UB after controlling for GA, birth weight, race, and sex. GA group was a significant effect modifier for the association between Ka and peak UB (0.03, 95% CI 0.02-0.04, P < .001). Interaction analyses showed the association between concomitant Ka and peak UB was significant for the 24-30 weeks GA group infants, but not for the 30-33 weeks GA group infants.

Conclusions: Peak UB was primarily associated with a decrease in binding affinity in infants ≤30 weeks GA. Interventions aimed at improving binding affinity may be important in decreasing the risk of bilirubin-induced neurotoxicity.