Radioimmunoassay of serum conjugated cholic acid

A radioimmunoassay for serum conjugated cholic acid is described using antiserum obtained five weeks after immunization of rabbits with cholic acid bovine serum albumin conjugate. Prior to the radioimmunoassay, extraction of bile acids was performed with Amberlite XAD-2. The displacement curve of glyco[3H]cholic acid was linear on a logit-log plot from 5 to 80 pmol of unlabelled glycocholic acid. Values for 8 normal fasting subjects ranged from 0.18 to 1.25 mumol/1. In 31 fasting subjects with or without liver disease serum values of conjugated cholic acid are related to serum bilirubin. Endoscopic retrograde cholangiopancreatography may influence serum levels of conjugated cholic acid.