Introduction Bile acid diarrhoea (BAD) is a common disorder which in the primary, idiopathic form may affect up to 1% of the population. 75Selenium Homocholic Acid Taurate (SeHCAT) 7 day retention is used in diagnosis, predicting faecal bile acid loss but is not available to primary care practitioners. The condition is chronic, causes significant morbidity and is easily treatable with bile acid sequestrants. Calprotectin is released into the intestinal lumen during neutrophil activation and apoptosis. A Faecal Calprotectin (FC) of >50 µg/g in the primary care setting has been reported to have a sensitivity and specificity of 82% and 77% respectively for organic GI disease.1In 2013 NICE recommended its use in primary care as a decision aid.2Since primary BAD does not have an inflammatory pathogenesis, we hypothesised that the faecal calprotectin test was not sensitive for bile acid diarrhoea.
Method Faecal calprotectin was measured in patients attending for SeHCAT testing at Imperial Healthcare NHS trust between March 2014 and July 2014. Patients with known bile acid diarrhoea, or inflammatory bowel disease were also recruited from the gastroenterology clinic during the same period. All patients had undergone lower GI endoscopy previously. Faecal samples were analysed in the Imperial Healthcare Biochemistry Laboratory using a commercially available ELISA kit (EliA, Phadia AB, Uppsala, Sweden).
Results 55 patients were recruited. Of these 32 (58%) were female, the mean age was 53 (range 23–88) and 41 (75%) had a SeHCAT scan, of which 25 (61%) were positive (<15% 7d retention). Overall 23 (42%) had a positive FC (>50 µg/g); 21 (38%) were known, or subsequently found to have traditional organic GI disease (14 Crohn’s, 3 ulcerative colitis, 1 radiation colitis, 3 hepatobiliary). 9 (22%) patients with a positive SeHCAT had a positive FC, all patients (n = 5, 12%) with IBD and a positive SeHCAT had a positive FC. If primary bile acid diarrhoea was excluded in the definition of organic disease, FC had a negative predictive value of 88% (95% CI: 71–96%) and a sensitivity and specificity of 83% (95% CI: 61–95%) and 88% (95% CI: 71–96%) respectively. However, if primary bile acid diarrhoea was included in the definition of organic disease, then FC has a negative predictive value of 43% (95% CI: 26–62%) and a sensitivity and specificity of 54% (35% CI: 37–70%) and 88% (95% CI: 62–98%) respectively.
Conclusion By including primary bile acid diarrhoea in the definition of organic disease the sensitivity of FC falls to 54%, which is unacceptable for a screening test. Patients with undiagnosed BAD are likely to be denied referral to secondary care for diagnosis and subsequent treatment due to the current guidance.
Disclosure of interest None Declared.
Polychronis P, et al. Scand J Gastroenterol. 2013;48:1048–1054
NICE diagnostics guidance 11, Issued Oct 2013
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