Variability of faecal calprotectin in inflammatory bowel disease patients: An observational case-control study

Background and Aims: Several factors have been reported to affect faecal calprotectin [FC] values, and significant variation in FC concentrations has been observed in inflammatory bowel disease [IBD] patients. We aimed to evaluate FC variability in IBD patients, and to assess the robustness of a single stool punch. Methods: This is a single-centre observational case-control study. Disease activity was assessed using endoscopic and clinical activity scores, as well as C-reactive protein levels. Stool samples were collected twice within a 1 to 6 days interval, and FC was measured on punches and homogenates by fluorometric enzyme immunocapture assay. Results: In all, 260 stool samples were collected from 120 patients. Intrastool variability was low, with an intraclass correlation coefficient for single measures between three punches from a single stool sample of 0.91, and median coefficient of variation [CV] of 17%. CV of two stool samples a few days apart [intra-individual variability] were significantly higher [p <0.01] with median CV of 36%. FC standard deviations correlated with mean FC levels either for intrastool or for intra-individual variability, with a Spearman's coefficient of rank correlation of 0.85 and 0.78, respectively [p