Introduction: Faecal calprotectin [FC] is a reliable surrogate marker for disease activity in ulcerative colitis [UC]; however, there are no consensus cut-off values for remission. The study aim was to correlate FC with Mayo Endoscopic Score [MES] and histological disease activity of UC patients in clinical remission. Methods: Our study recruited adult UC patients at the McGill IBD Center between 2013 and 2017. Patients in clinical remission [partial Mayo score ≤2], undergoing endoscopy for disease activity or dysplasia surveillance, were enrolled. Before bowel preparation, FC was collected. MES was documented during colonoscopy. Biopsies were taken; histological activity was assessed using Geboes score and the presence of basal plasmacytosis. Results: A total of 185 patients were recruited. The area under the curve [AUC] in receiver operating characteristic [ROC] analysis to predict MES 1-3 [from 0] was 0.743 [95% CI 0.67-0.82; p <0.001] with an FC cut-off value 170 μg/g [64% sensitivity, 74% specificity], and to predict MES 2-3 [from 0-1] was 0.722 [95% CI 0.61-0.83; p <0.001] with an FC cut-off value 170 μg/g [69% sensitivity, 65% specificity]. To differentiate MES 0 from MES 1, an FC value 130 μg/g yields a 70% sensitivity and 68% specificity. The AUC in ROC analysis to predict Geboes <3.1 was 0.627 [95% CI 0.55-0.71; p = 0.003], with an FC value 135 μg/g [54% sensitivity, 69% specificity]. Conclusions: In this large study, FC ≥170 μg/g predicts endoscopic activity and FC ≥135 μg/g predicts histological activity. Therefore in clinical practice, lower faecal calprotectin thresholds can be chosen to optimise identification of patients with ongoing endoscopic and histological disease activity.
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