GESTATIONL AGE AND CORD SERUM BILIRUBIN BINDING

Abstract

The effect of gestational age on bilirubin binding by albumin was studied using cord serum obtained from 22 preterm infants, 13 term infants and samples obtained from 17 adults. Using the horseradish peroxidase method, the apparent unbound bilirubin concentration (AUBC) was measured with increasing amounts of total bilirubin (TB). Serum albumin was also determined. The resultant bilirubin titration curve was analyzed using the least squares fit of the empiric equation Y = aXb and calculation of the association constants (Ka) using Scatchard plots.After correction for albumin concentration by plotting AUBC against the molar ratio of TB/albumin (R), term and preterm infants had identical curves while both were different than adults. At R of 0.6, AUBC for preterm infants was 46.1 nM/L ± 1.7 SEM; for term infants it was 49.8 nM/L ± 3.5 SEM (P=NS) and for adults it was 29.8 nM/L ± 1.6 SEM (both P <0.001). Using Scatchard plot analyses, the Ka1 for preterm infants and term infants was 0.39 ×109M−1 ± 0.05 SEM and 0.48 ×109M−1 ± 0.15 SEM (P=NS); for adult albumin Ka1 was 1.45 ×109M−1 ± 0.29 SEM (both P <0.01).We conclude that after correction for albumin concentration, bilirubin binding does not change with gestational age. Molecule for molecule the binding of cord albumin is the same for preterm and term infants. This suggests that infant albumin binds bilirubin less effectively than adult albumin.