Objective: To assess the reliability of serum 7 alpha-hydroxy-4-cholesten-3-one (7 alpha-3ox-C) in the differential diagnosis of bile acid induced diarrhoea by comparison with 75selenohomocholyltaurine whole body retention (SeHCAT WBR).
Design: One hundred and sixty-four patients with chronic diarrhoea were investigated prospectively in two centres (Edinburgh and Sweden) by two different tests which measure bile acid loss or synthesis: the SeHCAT test which measures the 7-day SeHCAT WBR and serum 7 alpha-3ox-C which reflects the rate of bile acid synthesis.
Results: Forty-six patients had SeHCAT WBR of less than 10% (19 with ileal disease or resection, nine with idiopathic bile acid induced diarrhoea and 18 with miscellaneous causes for bile acid induced diarrhoea). All patients with ileal or idiopathic disease showed a favorable response to treatment as did 13 of the miscellaneous group. Serum 7 alpha-3ox-C was raised in all subjects with ileal disease/resection, seven patients with idiopathic disease and all subjects in the miscellaneous group who responded to treatment. Sixteen out of 118 patients with SeHCAT WBR greater than or equal to 10% had raised serum 7 alpha-3ox-C.
Conclusion: The positive predictive value of serum 7 alpha-3ox-C was 74%. The high negative predictive value (98%) of serum 7 alpha-3ox-C indicates the possible use of this test for excluding bile acid malabsorption in this population. All but two subjects who responded to treatment had raised serum 7 alpha-3ox-C concentrations. The possibility that the sensitivity of the test can be improved by repeat testing needs to be further investigated. There was a significant correlation between fractional catabolic rate (FCR) SeHCAT and serum 7 alpha-3ox-C (r = 0.63, P < 0.0001). Further data are required to validate the reference range in women over 70 years of age.