P0329Fecal Calprotectin, Fecal Immunochemical Test, and Their Combination for Predicting Endoscopic and Histologic Remission in Clinically Quiescent Ulcerative Colitis

Background Fecal calprotectin (FC) is an established biomarker for assessing disease activity in ulcerative colitis (UC). However, the reported accuracy is 70-80% and may not be available in many centers. In contrast, the role of fecal immunochemical test (FIT), which is more available, remains limited. This study aimed to evaluate the diagnostic performance of FC, FIT, and the combination to predict endoscopic and histologic remission in patients with clinical remission. Methods A prospective cohort study was conducted between August 2023 and January 2025, enrolling adult patients with clinically quiescent UC (partial Mayo score <2). Stool samples were collected one day prior to the procedure and analyzed for FIT and FC levels. Correlations and diagnostic accuracies of FIT, FC, and their combination were assessed against Mayo endoscopic subscore; MES ≤1, MES 0, and histologic remission(Nancy score ≤1) using appropriate statistical methods. The cutoffs of 100 ng/mL and 150 mg/kg for FC were used based on previous studies and recommendations. Results Among the 67 participants (41.8% male; E1:E2:E3 = 9%: 51%: 40%), 44 (65.7%) achieved MES ≤1, 23 (34.3%) achieved MES 0, and 20 (29.9%) were in histologic remission. FIT and FC demonstrated a moderate positive correlation (ρ = 0.57, P<0.0001). The AUROC values of FIT versus FC were similar for predicting MES ≤1 (0.78 vs 0.74), while FIT showed slightly lower AUROC of 0.68 compared with 0.73 for MES 0, and 0.71 versus 0.79 for histologic remission. Table 1 summarizes the accuracy of FIT, FC, and combination testing across three endpoints. For predicting MES≤1, FIT demonstrated higher accuracy than FC (80.5% vs 59.7%; P=0.006), and their combination. However, there was no significant difference between the two tests in predictive MES 0 (58.2% for FIT vs 61.2% for FC; P=0.69). For histologic remission, FC performed better than FIT, although the difference was not statistically significant (53% for FIT vs. 68% for FC, P=0.07). Combining FIT with FC improved the prediction of histologic remission compared with FIT alone (P=0.01), but did not show an advantage over FC (P=0.16). Conclusion FC and FIT demonstrated good diagnostic accuracy for mucosal healing in UC. FIT is good in predicting MES ≤1 and may be reasonably used if FC is not available. However, FC appears to be superior to FIT in determining histologic remission. Conflict of interest: Dr. Chaemsupaphan, Thanaboon: No conflict of interest Salaemae, Marianee: No conflict of interest Sattayalertyanyong, Onuma: No conflict of interest Limsrivilai, Julajak: No conflict of interest