Measurement of bile acid kinetics in human serum using stable isotope labeled chenodeoxycholic acid and capillary gas chromatography electron impact mass spectrometry.

A non invasive method for measurement of bile acid kinetics in serum using (24-13C)chenodeoxycholic acid has been developed. After oral administration of 50 mg (24-13C)chenodeoxycholic acid, the exponential decay of the 13C atom percent excess was measured in serum using capillary gas chromatography mass spectrometry. This required that isotope ratios were measured with high accuracy and coefficients of variation less than 1% by means of selected ion monitoring and scan averaging. The clinical applicability was tested by repeated determination of pool size, fractional turnover and synthesis rate of chenodeoxycholic acid in one healthy volunteer. This method permitted the determination of pool size, synthesis and conversion of chenodeoxycholic acid into lithocholic acid in man without the use of radioactive tracers and without repeated duodenal intubation.