Enzymatic fluorimetric determination of cholic acid and chenodeoxycholic acid in aqueous solutions and blood serum using a differential kinetic method

An enzymatic fluorimetric method is described for the determination of chenodeoxycholic acid and its conjugates and of cholic acid and its conjugates in aqueous solutions and serum. The method is based on the oxidation of 7 α-hydroxy bile acids by β-NAD⁺ in the presence of 7 α-hydroxysteroid dehydrogenase; the NADH produced is monitored fluorimetrically. Chenodeoxycholic acid is determined in the presence of cholic acid by a differential kinetic procedure; the sum of the two acids (primary bile acids) is determined by an equilibrium procedure, and cholic acid is calculated by difference. The r.s.d. was ca. 3% and 10% for aqueous solutions and sera, respectively. Recoveries of chenodeoxycholic acid, cholic acid and primary bile acids added to serum samples averaged 100.5, 105.1, and 102.9%, respectively. Ten samples can be analyzed per working day.