Relationship of unbound bilirubin concentration to reserve albumin-binding concentration for bilirubin in human neonatal plasma.

We examined the relationship of plasma unbound bilirubin concentration and reserve albumin-binding concentration for bilirubin in a sample of 545 neonates. Plasma unbound bilirubin concentration and total bilirubin-binding concentration were determined with the peroxidase assay. Contrary to published reports, we found that plasma unbound bilirubin concentration and plasma reserve albumin for bilirubin-binding concentration are highly correlated (r = -0.706; p less than 0.001) and that the relationship between these two parameters is dependent upon the total bilirubin-binding concentration. That these measured parameters correlate in the same manner as predicted for free bilirubin and free albumin by the law of mass action, suggests that these measurements may be meaningful.