Adequate bowel preparation (BP) is crucial for high-quality colonoscopy surveillance in ulcerative colitis (UC), because an inadequate one leads to incomplete colonoscopy and higher rate of missing precancerous lesions, which are usually flat or subtle in this setting. There is conflicting evidence regarding risk factors for inadequate BP when UC patients are in endoscopic and clinical remission; furthermore, data on the optimal PEG-regimen which should be used in this setting are scarce. The aim of this study was to assess which factors influence the quality of BP in this specific setting.

This is a multicentre, cross-sectional, retrospective study carry out it eight centres between January-2021 and December-2022, including UC patients with endoscopic and clinical remission (Mayo endoscopic score=0) who underwent colonoscopy. Patients with colonic, ileal or abdominal surgery were excluded. The primary outcomes were the rate of adequate preparation, defined as total Boston Bowel Preparation Scale (BBPS) ≥6 with all segments scoring ≥2 and overall BBPS scores of patients undergoing BP with 1L-PEG-ASC (Plenvu®) and 2L-PEG (Moviprep®, Clensia®), without any specific allocation or instructions. Secondary endpoint was the evaluation of risk factors oof cleansing quality with a multivariable ordinal logistic regression, the right colon cleansing adequacy rate and exam completion rate.

Overall, 379 patients (mean age 52±15 years, 159 female) with quiescent UC undergoing colonoscopy stratified by preparation type: 1L-PEG (n=216) and 2L-PEG (n=163). Baseline clinical and demographic characteristics were compared. 1L-PEG yielded higher overall BP quality, with a significantly higher median total BBPS compared to 2L-PEG (8, IQR 7–9 vs 6, IQR 6–8, p<0.001). Although rate of adequate preparation was higher in the 1L-PEG group, this difference did not reach statistical significance (92.6% vs 87.7%, p=0.12). The 1L-PEG group demonstrated higher rates of exam completion (99.5% vs. 95.7%; p=0.02) compared to 2L-PEG, but no differences in overall right colon cleansing adequacy (96.3% vs 94.5%, p=0.46). At multivariate ordinal logistic regression adjusted for age, sex, and disease extension, the use of 2L-PEG was associated with significantly lower odds of achieving higher BBPS scores (OR 0.30, 95% CI 0.20–0.45) compared to 1L-PEG.

Conversely, patient demographics, smoking status, maximum disease extension, history of advanced therapy or presence of pseudopolyps did not significantly affect BP quality (p>0.05).

In a relatively unbiased setting, such as UC patients in endoscopic and clinical remission, 1L-PEG demonstrated better BP quality cleansing and higher procedural completion rates. Moreover, it was the primary determinant of BP quality, with neither disease extent nor a history of advanced therapy affecting BP. These findings suggest that 1L-PEG-ASC preparation may be the preferred option for colonoscopy BP in UC patients when not contraindicated.