Defining faecal calprotectin thresholds as a surrogate for endoscopic and histological disease activity in ulcerative colitis - a 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: remission1, active4; Nancy: remission1, active2; Combined criteria: remission UCEIS1 and Nancy1, active UCEIS4 and Nancy2). 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% 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, histologic, or combined criteria were 71g/g (range 8-624), 91g/g (range 8-858) and 67g/g (range 8-479), respectively. The FCal threshold above which active disease was confirmed was 187g/g for UCEIS (AUC 0.915), 72g/g for Nancy (AUC 0.824) and 187g/g for combined endoscopic and histologic 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 72g/g indicates histological inflammation (Nancy 2) and 187g/g indicates endoscopically active disease (UCEIS 4), whether combined with histopathology or not.