Accurate enzymatic measurement of fecal bile acids in patients with malabsorption

Quantitation of fecal bile acid excretion can help elucidate the cause of diarrhea or steatorrhea. Fecal bile acids can be measured with gas chromatography-mass spectrometry, but this is time-consuming, expensive, and not available for clinical use. Relatively simple enzymatic methods have been described for the measurement of fecal 3alpha-hydroxy bile acids, but these have not been validated in patients with gastrointestinal disease. We found that an enzymatic method yielded falsely low results in patients with malabsorption syndromes for two reasons: First, the preliminary hydrolysis step did not completely deconjugate bile acids, precluding their extraction into diethyl ether for enzymatic assay. Second, long-chain fatty acids inhibited 3alpha-hydroxysteroid dehydrogenase activity. By increasing the duration of hydrolysis and the concentration of enzyme, we developed a simple, accurate, and reproducible method for measuring fecal 3alpha-hydroxy bile acids that agreed well with values obtained with the use of gas chromatography-mass spectrometry (R = .95), both in normal subjects and in patients with malabsorption syndromes.