Risk Factors for Inadequate Bowel Preparation Before Colonoscopy in Patients with Ulcerative Colitis in Clinical and Endoscopic Remission: A Multicenter Retrospective Cohort Study

: Background/Objectives: Adequate bowel preparation (BP) is crucial for effective colorectal cancer (CRC) surveillance in ulcerative colitis (UC). While active inflammation is known to negatively impact cleansing, data regarding predictors of BP quality specifically in UC patients with inactive disease remain limited. This study aimed to investigate risk factors for inadequate BP in UC patients in clinical/endoscopic remission and to compare the efficacy of 1L-PEG-ASC versus 2L-PEG regimens. Methods: A multicentric, retrospective, cohort study was conducted across eight Italian centers. Consecutive adult outpatients with UC undergoing colonoscopy between January-2021 and December-2022 who were in endoscopic and clinical remission were included. Boston Bowel Preparation Scale (BBPS) was assessed in patients undergoing 1L-PEG-ASC or 2L-PEG bowel preparation. Univariable and multivariable logistic regression analyses were performed to identify risk factors for inadequate BP and compare outcomes between PEG regimens. Results: A total of 379 patients were included (58% M, mean age 52.3 ± 15.4 years). The overall rate of adequate BP was 90.5%. Traditional risk factors, including demographic, clinical, and endoscopic characteristics, were not predictive of inadequate preparation in this remission cohort. Comparing regimens, 1L-PEG-ASC yielded significantly higher median total BBPS scores compared to 2L-PEG (8 [IQR 7-9] vs. 6 [IQR 6-8]; p < 0.001) and a higher exam completion rate (99.5% vs. 95.7%; p = 0.02), although the difference in adequate BP rates did not reach statistical significance (92.6% vs. 87.7%; p = 0.12). Multivariable analysis confirmed that 2L-PEG was independently associated with lower odds of achieving higher BBPS scores (OR 0.30; 95% CI 0.20-0.45). Conclusions: In UC patients with clinical and endoscopic remission, BP adequacy rates are high and comparable to the general population, suggesting that traditional IBD-related risk factors are less relevant in the absence of active inflammation. However, the 1L-PEG-ASC regimen demonstrated superior cleansing quality and exam completion rates compared to 2L-PEG. These findings support the prioritization of 1L-PEG-ASC to optimize mucosal visualization during CRC surveillance in this population.