Experimental studies on unconjugated bilirubin binding by human erythrocytes.

The evaluation of the bilirubin bound to human erythrocytes is considered by some paediatricians as a test to estimate the risk of development of kernicterus. We have studied the physical and chemical characteristics of this binding. Red blood cell membranes contain specific binding sites for bilirubin, the affinity of which is low (Kd = 170 mumol/L). The dissociation constant of the bilirubin/human serum albumin complex is about 10,000 times lower. In jaundiced neonates even with a level of blood bilirubin higher than 300 mumol/l, the binding of bilirubin to red blood cells is negligible. So, the evaluation of the bilirubin bound to human red blood cells does not seem to be a useful test to appreciate the risk of development of kernicterus.