The synergy of dual faecal immunochemical and faecal calprotectin testing for accurate assessment of endoscopic and histological activity in inflammatory bowel disease.

Background: Faecal biomarkers are increasingly utilized for disease assessment in inflammatory bowel disease (IBD).

Objectives: To characterize the relative and combined accuracy of faecal calprotectin (FC) and faecal immunochemical testing (FIT) for detecting endoscopic and histologically active disease in Crohn's disease (CD) and ulcerative colitis (UC), subdivided by disease location.

Design: A prospective cohort study.

Methods: Patients with confirmed IBD undergoing routine ileocolonoscopy for activity assessment were prospectively recruited and performed both FC and FIT ±30 days of ileocolonoscopy. Endoscopic activity was assessed via the simplified endoscopic score for CD, Mayo endoscopic score for UC and histological activity graded as nil/mild/moderate. Receiver-operator curve analyses were utilized to assess the performance of FC and FIT per disease subtype and location.

Results: In all, 137 (79 CD, 57 UC) patients were recruited. FC was more sensitive than FIT in detecting active endoscopic (CD: 91% versus 69%, UC: 94% versus 82%) and histological (CD: 86% versus 55%, UC 88% versus 56%) disease. However, FIT was more specific than FC in detecting active endoscopic (CD: 94% versus 56%, UC: 85% versus 69%) and histological (CD: 93% versus 55%, UC: 96% versus 70%) diseases. FIT was more sensitive and specific than FC in detecting active colonic CD (endoscopic activity: 94% versus 93%, histological activity: 92% versus 77%, respectively); however, it was poorly sensitive for active ileal CD (43% versus 89%).

Conclusion: FC demonstrated higher sensitivity and FIT higher specificity for active IBD. Hence, dual testing was synergistic, displaying excellent performance characteristics across most IBD locations and subtypes, holding promise for future clinical application.

Trial registration: Not applicable.