BACKGROUND AND STUDY AIM: Inadequate colorectal cancer screening wastes limited endoscopic resources. We examined patients factors associated with inadequate flexible sigmoidoscopy (FSG) screening at baseline screening and repeat screening 3-5 years later in 10 geographically-dispersed screening centers participating in the ongoing Prostate, Lung, Colorectal, and Ovarian Cancer Screening Trial.

METHODS: A total of 64,554 participants (aged 55-74) completed baseline questionnaires and underwent FSG at baseline. Of these, 39,385 participants returned for repeat screening. We used logistic regression models to assess factors that are associated with inadequate FSG (defined as a study in which the depth of insertion of FSG was <50 cm or visual inspection was limited to <90% of the mucosal surface but without detection of a polyp or mass).

RESULTS: Of 7084 (11%) participants with inadequate FSG at baseline, 6496 (91.7%) had <50 cm depth of insertion (75.3% due to patient discomfort) and 500 (7.1%) participants had adequate depth of insertion but suboptimal bowel preparation. Compared to 55-59 year age group, advancing age in 5-year increments (odds ratios (OR) from 1.08 to 1.51) and female sex (OR = 2.40; 95% confidence interval (CI): 2.27-2.54) were associated with inadequate FSG. Obesity (BMI > 30 kg/m(2)) was associated with reduced odds (OR = 0.67; 95% CI: 0.62-0.72). Inadequate FSG screening at baseline was associated with inadequate FSG at repeat screening (OR = 6.24; 95% CI: 5.78-6.75).

CONCLUSIONS: Sedation should be considered for patients with inadequate FSG or an alternative colorectal cancer screening method should be recommended.