Determination of cholic and chenodeoxycholic acid in serum: evaluation of two commercial radioimmunoassay methods.

Commercially available radioimmunoassay kits for determination of serum cholic and chenodeoxycholic acid conjugates ("Glycocholic acid RIA kit", "Glycochenodeoxycholic acid RIA kit",. Nordiclab Oy, Oulu, Finland) have been evaluated with respect to recovery, specificity and precision. The recovery of the glycocholic acid method was low when performed according to the manufacturer's instructions, but could be raised to an acceptable level by using serum-based standards. However, the non-specific binding of serum samples varied considerably in the glycocholic acid method and would demand the use of individual blanks. The recovery of the glycochenodeoxycholic acid method was satisfactory and no inter-individual serum effect was discovered. The methods were considered sufficiently specific for their purposes, but precision was rather low for values within the lower normal range in both methods. We conclude that the glycochenodeoxycholic acid method is satisfactory for its purpose, but the glycocholic acid method needs to be modified.