Prediction of endoscopic disease activity in ulcerative colitis by two different assays for fecal calprotectin

As mucosal healing is the goal of treatment in inflammatory bowel disease, defining a fecal [f-] calprotectin cut-off level for mucosal healing is crucial. Previous studies have presented different cut-off levels. The aim of this study was to investigate the ability of two f-calprotectin assays to differentiate mucosal healing from inflammation in ulcerative colitis.

Sixty-two patients with ulcerative colitis underwent colonoscopy for classification of mucosal inflammation [Mayo endoscopic subscore]. The patients also submitted a fecal sample for f-calprotectin analysis using two different assays, Calpro ELISA and Buhlmann ELISA.

The two assays correlated significantly, with a Spearman rank correlation coefficient of 0.86. Both assays showed significantly different f-calprotectin levels in patients with a Mayo endoscopic subscore of 0 [mucosal healing] and 1–3 [inflamed mucosa] [p <0.001]. Using ROC curve analyses, we selected the best cut-off levels for both assays with responding sensitivity and specificity [presented with 95% confidence intervals]; Calpro ELISA cut-off 61 μg/g, sensitivity 84.1% [75.0–93.2%], specificity 83.3 % [74.0–92.6%], and Buhlmann ELISA cut-off 96 μg/g, sensitivity 90.9 % [83.7–98.1%], specificity 83.3 % [74.0–92.6%]. Defining mucosal healing as a Mayo endoscopic subscore ≤1, cut-off levels increased: Calpro ELISA cut-off 110 μg/g, sensitivity 80.0%[70–90%], specificity 66.6 % [54.9–78.3%]; and Buhlmann ELISA cut-off 259 μg/g, sensitivity 83.3 %[74–92.6%], specificity 71.9 % [60.7–83.1%].

The study demonstrates the need for assay specific cut-off levels in clinical practice,as the f-calprotectin cut-off level for endoscopic disease activity differed in these two assays.