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 (DeltaB(T)) would increase significantly with increasing binding avidity. METHODS: The plasma total bilirubin concentration (B(T)), 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. DeltaB(T) (in milligrams per deciliter per hour) was calculated as the slope of B(T) 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 DeltaB(T) would increase significantly with K.albumin concentration. RESULTS: The ranges of B(T), 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 mug/dL, 2.9 to 4.6 g/dL, and 38 to 163 L/mumol, respectively. DeltaB(T) correlated significantly with K.albumin concentration (r(2) = 0.23; P = .026). CONCLUSIONS: Plasma bilirubin binding avidity contributes significantly to DeltaB(T). This component of DeltaB(T) 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. [ABSTRACT FROM AUTHOR]