Faecal calprotectin is the biomarker that best distinguishes remission from different degrees of endoscopic activity in Crohn's disease.

Background: Effective control of the inflammatory process in Crohn's disease (CD) is reflected in intestinal mucosal healing. The performances of faecal calprotectin (fcal), clinical and serologic parameters in the inflammatory activity evaluation and their correlation to the simple endoscopic score (SES-CD) are the goals of this study.

Methods: Patients with CD referred for ileocolonoscopy were prospectively included and distributed according to the degree of endoscopic inflammatory activity into remission, mild activity, and moderate to severe activity groups. The different degrees of endoscopic activity were correlated with the following indexes: Crohn's disease activity index (CDAI), fCal, serum C-reactive protein (CRP), and haemogram. The control group comprised individuals without known intestinal disease who were referred for colorectal cancer screening.

Results: Eighty colonoscopies were performed in patients with CD and 21 in the control group. The control group had a lower median fCal (59.7 mcg/g) than patients with CD (683 mcg/g, p < 0.001). A moderate Spearman correlation occurred between SES-CD and CRP (r = 0.525), fCal (r = 0.450), and CDAI (r = 0.407), while a weak correlation was found with the platelet count (r = 0.257). Only fCal distinguished patients in remission from those with mild activity (236.6 mcg/g × 654.9 mcg/g, p = 0.014) or moderate to severe activity (236.6 mcg/g × 1128 mcg/g, p < 0.001). An fCal cut-off of 155 mcg/g was sensitive (96%) and accurate (78%) for the diagnosis of endoscopic activity.

Conclusions: fCal provides greater diagnostic accuracy than the other activity markers for endoscopic activity of patients with CD, moderate correlation to SES-CD, and a capacity to discriminate patients in remission from those with mild or moderate to severe activity.