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

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 (B_Total), which is currently used to guide clinical care; the bilirubin binding capacity (BBC); and the concentration of non-albumin bound or free bilirubin (B_Free). The fourth component is the bilirubin-albumin equilibrium dissociation constant, K_D, which is calculated from B_Total, BBC, and B_Free 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 B_Total) are needed to expedite the clinical use of bilirubin binding. At any B_Total, the B_Free and the relative risk of bilirubin neurotoxicity increase as the K_D/BBC ratio increases (ie, bilirubin binding worsens). Comparing the K_D/BBC ratio of newborns with B_Total of concern with that typical for the population helps determine whether the risk of bilirubin neurotoxicity varies significantly from the inherent risk at that B_Total Furthermore, the bilirubin binding panel individualizes care because it helps to determine how aggressive intervention should be at any B_Total, irrespective of whether it is above or below established B_Total guidelines. The bilirubin binding panel may reduce anxiety, costs, unnecessary treatment, and the likelihood of undetected bilirubin neurotoxicity.