Adherence to colorectal cancer screening measured as the proportion of time covered

Background and Aims: Colorectal cancer (CRC) screening can reduce CRC incidence and mortality, but measuring screening adherence over time is challenging. We examined adherence using a novel measure characterizing the proportion of time covered (PTC) by screening tests. Methods: Eligible patients were age 50 to 60 years and followed at a large, safety-net health care system between January 2010 and September 2014. We estimated PTC as the number of days up to date with screening divided by the number of days from cohort entry until study end, CRC diagnosis, or death. We estimated mean and median PTC and used least-significant difference tests to assess differences in adherence by patient characteristics. Results: Of 18,257 patients, most were non-Hispanic black (40.5%) or Hispanic (34.9%) and/or female (62.4%). Approximately 40% (n = 7559) were never screened during the study period; the remaining 10,698 patients completed 19,105 screening examinations (14,481 fecal immunochemical tests [FITs], 4393 colonoscopies, 94 sigmoidoscopies, and 137 barium enemas). Overall, the mean PTC was 29.1% (95% confidence interval [CI], 28.6%-29.5%). Among those who completed at least one screening test (n = 10,698), the mean PTC was 49.0% (95% CI, 48.5%-49.5%). The most common reasons for non-adherence were lack of repeat FIT and no diagnostic colonoscopy after abnormal results for the FIT. The mean PTC increased with the number of primary care visits (0 visits, 21%; 1 visit, 29%; 2-3 visits, 35%; ≥4 visits, 37%; all P <.05). Conclusions: PTC provides a reliable estimate of screening adherence, capturing breakdowns in the CRC screening process amenable to intervention. Repeat FIT and diagnostic colonoscopy are important intervention targets that may increase adherence in underserved populations.