Bilirubin binding in premature infants from birth to 3 months.

The effect of postnatal age on serum bilirubin binding measurements was studied prospectively in extremely premature infants of 25-28 weeks' gestation. Serum was obtained from 10 infants at birth, 2-4 days of age, 1 week, 2 weeks, 4 weeks, 8 weeks, and 10-13 weeks. Using peroxidase oxidation, the apparent unbound bilirubin concentration (AUBC) was measured and plotted versus the molar ratio of total bilirubin:albumin (R) using the empiric power curve AUBC = aRb. The apparent unbound bilirubin concentration at bilirubin:albumin ratio 0.6 was used to compare relative binding ability among specimens. This value, as well as the apparent association constants, showed dramatic deterioration after birth, which persisted without improvement until 8 weeks of age. This pattern of recovery correlated in general with the resolution of clinical problems. Binding values equivalent to adult serum were achieved by 10-13 weeks. This study emphasises that diminished bilirubin binding by the sera of premature infants can persist for a prolonged period.