BackgroundColonoscopy is the standard and most effective screening tool for colonic diseases and the accuracy of colonoscopy depends on the quality of bowel preparation. The aim of this study was to analyze the risk factors for inadequate bowel preparation before colonoscopy.MethodsIn this retrospective study, patients who underwent colonoscopy in 2018 and received 3 L of Polyethylene Glycol Electrolytes powder were included. They were instructed to drink 1.5 L the night before the colonoscopy and 1.5 L 4–6 h before the procedure given in doses of 250 ml every 10 min with 30 ml of simethicone given 4–6 h before the colonoscopy. Patient- and procedure-related parameters were recorded. An adequate bowel preparation was defined as all 3 segments rated 2 or 3 on the Boston Bowel Preparation scale. Risk factors for inadequate bowel preparation were identified using multivariate logistic regression analysis.ResultsA total of 6720 patients were included in the present study. The mean age of these patients was 49.7 ± 13.0 years old. Inadequate bowel preparation was found in 233 (12.4%), 139 (6.4%), 131 (7%), 68 (8.6%) patients in spring, summer, autumn and winter respectively. On the multivariate analysis, male gender (OR: 1.295; 95% CI: 1.088–1.542; P = 0.005), inpatient status (OR: 1.377; 95% CI: 1.040–1.822; P = 0.025) and season (spring vs. winter, OR: 1.514; 95% CI: 1.139–2.012; P = 0.004) were the independent risk factors for inadequate bowel preparation.ConclusionsMale gender, inpatient status and spring season were the independent risk factors for inadequate bowel preparation. For patients with risk factors for inadequate bowel preparation, enhanced bowel preparation and instructions may help to optimize the quality of bowel preparation.