Unrestricted faecal calprotectin testing performs poorly in the diagnosis of inflammatory bowel disease in patients in primary care

BACKGROUND: Faecal calprotectin (FC) measurement distinguishes patients with inflammatory bowel disease (IBD) from those with irritable bowel syndrome but evidence of its performance in primary care is limited. AIMS: To assess the yield of IBD from FC testing in primary care. METHODS: Retrospective review of hospital records to assess the outcome following FC testing in primary care. Investigations for all patients undergoing FC testing in a single laboratory for 6 months from 1 October 2013 to 28 February 2014 were reviewed. RESULTS: 410 patients (162 male; median age 42; range 16-91) were included. FC>50 µg/g was considered positive (FC+). 148/410 (36.1%; median age 44 (17-91)) were FC+ (median FC 116.5 µg/g (51-1770)). 122/148 FC-positive patients (82.4%) underwent further investigation. 97 (65.5%) underwent lower gastrointestinal endoscopy (LGIE), of which 7 (7.2%) had IBD. 49/262 (18.7%) FC-negative (FC-) patients (FC ≤50 µg/g) (median age 47 (19-76)) also underwent LGIE, of whom 3 (6.1%) had IBD.IBD was diagnosed in 11/410 (2.7%; 4 ulcerative colitis, 3 Crohn's disease, 4 microscopic colitis). 8/11 were FC+ (range 67-1170) and 3 FC-. At a 50 µg/g threshold, sensitivity for detecting IBD was 72.7%, specificity 64.9%, positive predictive value (PPV) 5.41% and negative predictive value 98.9%. Increasing the threshold to 100 µg/g reduced the sensitivity of the test for detecting IBD to 54.6%. CONCLUSIONS: FC testing in primary care has low sensitivity and specificity with poor PPV for diagnosing IBD. Its use needs to be directed to those with a higher pretest probability of disease. Local services and laboratories should advise general practitioners accordingly.