The Bilirubin Binding Panel: A Henderson-Hasselbalch Approach to Neonatal Hyperbilirubinemia

Abstract

Poor plasma bilirubin binding increases the risk of bilirubin neurotoxicity in newborns with hyperbilirubinemia. New laboratory tests may soon make it possible to obtain a complete bilirubin binding panel when evaluating these babies. The 3 measured components of the panel are the plasma total bilirubin concentration (BTotal), which is currently used to guide clinical care; the bilirubin binding capacity (BBC); and the concentration of non–albumin bound or free bilirubin (BFree). The fourth component is the bilirubin-albumin equilibrium dissociation constant, KD, which is calculated from BTotal, BBC, and BFree. The bilirubin binding panel is comparable to the panel of components used in the Henderson-Hasselbalch approach to acid-base assessment. Bilirubin binding population parameters (not prospective studies to determine whether the new bilirubin binding panel components are better predictors of bilirubin neurotoxicity than BTotal) are needed to expedite the clinical use of bilirubin binding. At any BTotal, the BFree and the relative risk of bilirubin neurotoxicity increase as the KD/BBC ratio increases (ie, bilirubin binding worsens). Comparing the KD/BBC ratio of newborns with BTotal of concern with that typical for the population helps determine whether the risk of bilirubin neurotoxicity varies significantly from the inherent risk at that BTotal. Furthermore, the bilirubin binding panel individualizes care because it helps to determine how aggressive intervention should be at any BTotal, irrespective of whether it is above or below established BTotal guidelines. The bilirubin binding panel may reduce anxiety, costs, unnecessary treatment, and the likelihood of undetected bilirubin neurotoxicity.