P0265Optimizing Fecal Calprotectin Thresholds for Endoscopic Activity in Ulcerative Colitis

Abstract Background Fecal calprotectin (FC) is a reliable biomarker for intestinal inflammation in ulcerative colitis (UC), but objective cutoff values reflecting endoscopic activity remain uncertain. This study aimed to define clinically meaningful FC thresholds corresponding to endoscopic disease severity. Methods We conducted a retrospective single center study to identify fecal calprotectin (FC) thresholds reflecting endoscopic activity in ulcerative colitis (UC). Adult patients who underwent colonoscopy between January 2020 and December 2024 and had FC measured within 30 days before colonoscopy were included from the institutional Clinical Data Warehouse. FC values were standardized to µg/g, with non-numeric results (e.g., “0.1,” “6000”) converted to boundary values. Endoscopic activity was assessed using the Mayo Endoscopic Subscore (MES) and the Ulcerative Colitis Endoscopic Index of Severity (UCEIS). Receiver operating characteristic (ROC) analyses were performed to determine optimal FC cutoffs for MES 0 vs ≥ 1, ≤1 vs ≥ 2, and ≤2 vs 3; and for UCEIS ≤1 vs ≥ 2, ≤4 vs ≥ 5, and ≤6 vs ≥ 7. Cutoffs were derived using Youden’s J index with bootstrapped 95% confidence intervals (CIs). Results A total of 519 UC patients contributed 589 MES and 582 UCEIS-paired FC measurements. The median interval between stool collection and colonoscopy was 0 days (mean 3.9). FC levels increased stepwise with endoscopic severity. Mean FCs for MES 0–3 were 45, 213, 477, and 1205 µg/g, respectively. For UCEIS 0–8, mean FC rose from 43 µg/g (UCEIS 0) to 1663 µg/g (UCEIS 7). ROC analyses demonstrated strong discriminatory performance. For MES, AUCs were 0.81 (95% CI, 0.78–0.84), 0.80 (0.76–0.84), and 0.85 (0.81–0.89), with optimal cutoffs of 75, 106, and 293 µg/g, respectively. For UCEIS, AUCs were 0.82 (0.79–0.85), 0.86 (0.81–0.90), and 0.85 (0.79–0.92), yielding similar thresholds of 88, 276, and 333 µg/g. Conclusion Fecal calprotectin correlated strongly with endoscopic activity in ulcerative colitis. Based on the Mayo score, FC thresholds of 75, 106, and 293 µg/g effectively differentiated inactive, moderate, and severe inflammation. Comparable values using the UCEIS (90, 280, and 330 µg/g) confirmed the robustness and reproducibility of these findings. FC can therefore serve as a practical, noninvasive surrogate for mucosal disease activity and a useful tool for treat-to-target monitoring in ulcerative colitis. References: Inflamm Bowel Dis. 2025 Sep 19:izaf008. Intestinal Research 2025;23(2):144-156. JGH Open. 2018 Aug 10;2(5):207–213. Inflamm Bowel Dis. 2024 Dec 5;30(12):2347-2355. Jain et al. BMC Gastroenterology (2025) 25:429. Conflict of interest: Prof. Kim, Ji Eun: No conflict of interest Lee, Yeong Chan: No conflict of interest Hong, Sung Noh: Grant: National Research Foundation of Korea (NRF) grant funded by the Korea government (MSIP) (2019R1A2C2010404) Future Medicine 20*30 Project of the Samsung Medical Center. Kim, Minjee: No conflict of interest Kim, Eun Ran: No conflict of interest Chang, Dong Kyung: No conflict of interest Kim, Young-Ho: No conflict of interest