ABSTRACT
BACKGROUND: A strong correlation between the bilirubin/albumin (B/A) ratio and unbound bilirubin (UB) levels in newborns ≥35 weeks of gestation has been reported. However, in preterm infants, the usefulness of B/A ratios remains unclear. METHODS: We obtained serum from 381 newborns <35 weeks of gestation. UB levels were measured using the glucose oxidase-peroxidase method. Total serum bilirubin (TB) and albumin (Alb) concentrations were measured spectrophotometrically. Samples were then stratified into two groups based on the infant's phototherapy use. B/A ratios were calculated and correlated with UB levels. Samples taken from infants prior to or never receiving phototherapy (No PTx) were then stratified by gestational age (GA) epochs: 22-27, 28-29, 30-31, and 32-34 weeks and B/A ratios correlated with UB levels. RESULTS: B/A ratios significantly correlated with UB levels in samples from the No PTx cohort (n = 1250; y = 1.83x - 0.15, r2 = 0.93) when compared with samples from infants post-phototherapy (Post-PTx, n = 2039; y = 1.05x + 0.09, r2 = 0.69). Even when stratified by GA, the correlation remained. CONCLUSIONS: In preterm infants <35 weeks of gestation, B/A ratios correlated with UB levels better in infants prior to or never receiving phototherapy than in those infants receiving phototherapy. IMPACT: The bilirubin/albumin (B/A) ratio significantly correlates with unbound bilirubin (UB) levels in preterm infants <35 weeks of gestation. The B/A ratio can be used as an index of UB levels in preterm infants <35 weeks of gestation. The B/A ratio is useful, especially when UB measurements are not available, for managing hyperbilirubinemia in preterm infants.