BACKGROUND This study prospectively evaluated the risk of relapse according to the status of histologic activity in patients with ulcerative colitis (UC) who achieved deep remission.

METHODS Patients with UC in clinical remission (partial Mayo score ≤1) and endoscopic remission (ulcerative colitis endoscopic index of severity ≤1) were enrolled. Rectal biopsies were performed in patients, and histologic remission was defined as a Robarts histopathology index of ≤3. Receiver-operating characteristic curve analysis was conducted to determine fecal calprotectin cutoff values for histologic remission. The cumulative risk of relapse was evaluated using the Cox proportional hazards model.

RESULTS Among the 187 patients enrolled, 82 (43.9%) achieved histologic remission. The best cutoff value of fecal calprotectin for predicting histologic remission was 80 mg/kg (area under the curve of 0.646, sensitivity of 74%, and specificity of 61%). Among 142 patients who were followed up for >3 months, 56 (39.4%) showed clinical relapse during a median of 42 weeks. The risk of relapse was lower in patients with histologic remission than in those with histologic activity (P = .026). In multivariable analysis, histologic remission (hazard ratio [HR], 0.551; 95% confidence interval [CI], 0.316-0.958; P = .035), elevated C-reactive protein levels (HR, 3.652; 95% CI, 1.400-9.526; P = .008), and history of steroid use (HR, 2.398; 95% CI, 1.196-4.808; P = .014) were significantly associated with clinical relapse.

CONCLUSIONS In patients with UC who achieved clinical and endoscopic remission, histologic remission was independently associated with a lower risk of clinical relapse.