Development of a spin assay for reserve bilirubin loading capacity of human serum.

The capacity of human serum albumin to bind bilirubin is of paramount importance in the prevention of neurological damage due to hyperbilirubinemia in the neonate. Currently, there is no rapid, reliable method to determine the reserve bilirubin loading capacity of serum albumin. A method using electron spin resonance spectroscopy with a dianionic spin-label molecular probe [1-N-(2,2,6,6-tetramethyl-1-oxyl-4-piperidinyl)-5-N-(1-aspartate)-2,4-dinitrobenzene] is presented which yields the reserve binding capacity of the bilirubin high-affinity binding site on human serum albumin and reserve bilirubin loading capacity of serum in mg/dl. Clinical validation of this spin assay may improve the neonatal care of jaundiced newborns.