Factors Affecting the Relationship Between Total and Unbound Bilirubin in Preterm and Term Infants.

Objective: Newborn infants universally experience jaundice, most of which is physiologic, but in some high-risk situations, it may lead to neurological dysfunction or death. Unbound bilirubin (Bf) may be the best predictor of bilirubin toxicity in this population. The goal of the study is to examine the relationship between total serum bilirubin (TSB) and Bf and the influencing factors.

Methods: To calculate the relationship of Bf to TSB, we created a ratio (R) Bf/TSB × 106 to allow the comparison of products with varied concentrations. We then applied it to simultaneously obtain TSB and Bf measurements in infants to examine the influence of prematurity, haemolysis, feeding (breast or bottle feedings) and phototherapy. We also examined R at potential toxic Bf levels in the preterm group.

Results: The population consisted of 170 term and 130 preterm infants. The R was 3.64 ± 1.08 (SD) in term and 15.18 ± 9.8 in preterm infants. Prematurity and high TSB that required phototherapy significantly increased R. Higher R-values were seen at higher Bf toxic threshold levels.

Conclusions: An R-value can reflect the relationship between Bf and TSB. The values are greater in prematurity and in infants with high TSB, which requires phototherapy.