A Crohn’s Conundrum: Can the Faecal Calprotectin Level Act as a Sensitive Cut-off to Prevent Unnecessary MRI Small Bowel Scans?

Abstract

Background: Current gastroenterology practice in evaluating those with diarrhoeal symptoms
and a positive faecal calprotectin (CP) is to perform colonoscopy. Colonoscopy however is
limited, in that it cannot exclude disease proximal to the terminal ileum. Therefore, for many
patients not known to have Crohn’s disease, gastroenterologists are often concerned about the
possibility of more proximal small bowel Crohn’s and request an magnetic resonance imaging
(MRI) small bowel scan.
Aims: This is the first study to investigate whether patients with a clinical suspicion of Crohn’s
but with a normal colonoscopy will benefit from MRI in terms of diagnostic evaluation if they
have a CP below the cut-off.
Method: MRI small bowel reports, CP levels and colonoscopy reports were analysed (where
obtainable) from 422 scans at a district general hospital in Stevenage, between 02/04/2015 and
21/07/2017. Eighty-five patients had features suggestive of Crohn’s but had normal colonoscopy
findings. These were divided into those who had a CP above or below 600.
Results: Within 55 patients who had a calprotectin below 600, we report that none (0%) of
these patients were found to have significantly positive findings for Crohn’s on subsequent
MRI. Amongst 30 patients with a positive CP, 8 (26.6%) were found to have active disease on
MRI. The sensitivity of calprotectin was therefore identified to be 100% (95% CI 63.06% to
100%) and the specificity of the test was 71.43 % (95% CI 60% to 81.15%). Negative predictive
value (NPV) was 1.00 and positive predictive value (PPV) was 0.27.
Conclusion: Our study is the first to suggest that in patients with features of Crohn’s who have
a normal colonoscopy, calprotectin performs impressively as a sensitive marker of the presence
of small bowel inflammation on subsequent MRI. Further prospective studies would be needed
to validate a potential approach of using the biomarker as a cut-off to reduce unnecessary MRI
small bowel scans.