The Crohn's disease activity index (CDAI) is similarly elevated in patients with Crohn's disease and in patients with irritable bowel syndrome

While the Crohn's disease activity index (CDAI) is the gold standard for defining clinical endpoints in Crohn's disease (Crohn's) clinical trials, its ability to distinguish symptoms due to inflammation from those that are non-inflammatory has been questioned.To compare CDAI scores in patients with Crohn's and those with Irritable Bowel Syndrome (IBS).This was a prospective, cross-sectional cohort study of 91 patients with either Crohn's (n = 44) or IBS (n = 47). Total CDAI and individual component scores were recorded and comparisons were made between Crohn's and IBS patients.Mean CDAI scores were higher in the IBS patients (183 vs. 157, P = 0.1). Sixty-two per cent (n = 29) of IBS patients had CDAI scores greater than 150. Mean CDAI haematocrit score (35.9 vs. 23.0, P = 0.02) and CRP level (6.8 vs. 2.0, P = 0.002) were higher in the Crohn's group. Analysis of CDAI sub-scores demonstrated that IBS patients had significantly higher pain (mean 1.7 vs. 0.8, P = 0.0007) and well-being scores (mean 1.2 vs. 0.8, P = 0.04) relative to patients with Crohn's. Specifically evaluating patients with CDAI greater than 150 (n = 51), IBS patients had higher pain sub-scores (mean 2.4 vs. 1.4, P = 0.002), whereas patients with Crohn's had higher CRP (mean 8.4 vs. 1.8, P = 0.001).Our study demonstrates that the CDAI does not discriminate patients with symptoms due to active Crohn's from patients with IBS. Patients with IBS can have CDAI scores in the clinically meaningful range. Objective measures, such as CDAI haematocrit score and CRP, are more specific markers of inflammation.