Risk Factors Associated with Inadequate Bowel Preparation in Patients with Functional Constipation

Background Constipation is a common reason of poor bowel preparation, which negatively influences the quality of colonoscopy. Risk factors for inadequate bowel preparation in constipated patients remain unclear. Aims This study aimed to investigate the high-risk factors that might influence the quality of bowel preparation in patients with functional constipation. Methods Consecutive patients with functional constipation who underwent colonoscopy between June 2016 and April 2017 were enrolled. A standard split dose of 4 l polyethylene glycol was used for bowel preparation. Patient- and procedure-related parameters were recorded. The primary outcome was an adequate rate of bowel preparation. Risk factors for inadequate bowel preparation were screened by multivariate logistic regression analysis. Results A total of 199 patients were included. Adequate bowel preparation was found in 62.8% (125/199) of patients. At multivariate analysis, Bristol stool form scale (BSFS) 1 [odds ratio (OR) 2.73, 95% confidence interval (CI) 1.26-5.90; P = 0.011], rectal pain score during defecation < 2 (OR 4.14, 95% CI 1.22-13.97; P = 0.022), and starting-to-defecation interval >= 4 h (OR 3.83, 95% CI 1.34-10.91; P = 0.012) were risk factors for inadequate bowel preparation in patients with constipation. For patients with no, 1, 2, or 3 risk factors, the rates of inadequate bowel preparation were 11%, 23%, 49%, and 65%, respectively. Conclusions With the standard preparation regime, > 1/3 of patients with functional constipation had inadequate bowel cleansing. BSFS 1, rectal pain score during defecation < 2, and starting-to-defecation interval >= 4 h were identified as independent risk factors for inadequate bowel preparation in constipated patients.