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Bilirubin Binding Contributes to the Increase in Total Bilirubin Concentration in Newborns With Jaundice

OBJECTIVE: This study tests the hypothesis that the hourly rate of increase in plasma bilirubin concentration (ΔBT) would increase significantly with increasing binding avidity. METHODS: The plasma total bilirubin concentration (BT), unbound bilirubin concentration, and albumin concentration values for healthy newborns with jaundice (≤100 hours of age, ≥35 weeks of gestation, and ≥2.5 kg at birth) were obtained from medical records. ΔBT (in milligrams per deciliter per hour) was calculated as the slope of BT versus age (in hours). Binding avidity was quantified as the product of the albumin concentration and its bilirubin binding constant (K). Linear correlation was used to test the hypothesis that ΔBT would increase significantly with K·albumin concentration. RESULTS: The ranges of BT, unbound bilirubin concentration, albumin concentration, and K values for the 21 patients studied were 7.6 to 28.5 mg/dL, 0.53 to 2.52 μg/dL, 2.9 to 4.6 g/dL, and 38 to 163 L/μmol, respectively. ΔBT correlated significantly with K·albumin concentration (r2 = 0.23; P = .026). CONCLUSIONS: Plasma bilirubin binding avidity contributes significantly to ΔBT. This component of ΔBT is associated with a lower risk of bilirubin neurotoxicity, and studies aimed at incorporating plasma bilirubin binding avidity measurements into the algorithms used for management of newborn jaundice seem warranted.