Defining Faecal Calprotectin Thresholds as a Surrogate for Endoscopic and Histological Disease Activity in Ulcerative Colitisa Prospective Analysis

Background Faecal calprotectin [FCal] levels are used as a surrogate marker for mucosal inflammation, but thresholds for defining endoscopic or histological disease activity in ulcerative colitis [UC] remain unclear. Methods Using validated indices, prospective measurements of FCal, symptoms [Simple Colitis Clinical Activity Index, SCCAI], endoscopic [Ulcerative Colitis Endoscopic Index of Severity, UCEIS] and histological activity [Nancy index] were made over 6 months in patients enrolled into the TrueColours UC web-based monitoring programme. Repeated measurements correlation was performed between FCal and SCCAI, UCEIS, and Nancy indices using definitions for remission and active disease [UCEIS: remission 1, active 4; Nancy: remission 1, active 2; combined criteria: remission UCEIS 1 and Nancy 1, active UCEIS 4 and Nancy 2]. Receiver operating characteristic curves investigated FCal thresholds after maximising sensitivity for active disease. Results In 39 patients followed prospectively for 6 months, correlation coefficients between FCal and SCCAI, UCEIS, and Nancy indices were 0.271 (95% confidence interval [CI] 0.114-0.415), 0.741 [95% CI 0.289-0.922], and 0.876 [95% CI 0.605-0.965], respectively. Median FCal thresholds for remission using endoscopic, histological, or combined criteria were 71 g/g [range 8-624], 91 g/g [range 8-858], and 67 g/g [range 8-479], respectively. The FCal threshold above which active disease was confirmed was 187 g/g for UCEIS (area under the curve [AUC] 0.915), 72 g/g for Nancy [AUC 0.824], and 187 g/g for combined endoscopic and histological criteria [AUC 0.936]. Conclusions Correlation between FCal and symptoms in UC is weak. In contrast, the correlation between FCal and endoscopic or histological activity is strong. An FCal 72 g/g indicates histological inflammation [Nancy 2] and 187 g/g indicates endoscopically active disease [UCEIS 4], whether combined with histopathology or not.