Impact of a Failsafe Reminder Letter and Associated Factors on Correct Follow-Up After a Positive FIT in the Flemish Colorectal Cancer Screening Program

Background: Timely diagnostic colonoscopy (DC) after a positive fecal immunochemical test (FIT+) is essential for effective colorectal cancer (CRC) screening. In Flanders, 16% of FIT+ participants in 2022 had no DC in the 24 months following the FIT+ result. This study evaluated the impact of a failsafe reminder letter—sent 24 months after a FIT+ result without registered correct follow-up—on DC completion and identified factors associated with correct follow-up. Methods: We included all individuals in the Flemish CRC screening program who had a FIT+ result between 2017 and 2019 and later received a failsafe letter due to lacking correct follow-up within 24 months. Correct follow-up was defined as a complete colonoscopy, virtual colonoscopy, or cancer diagnosis. We calculated the proportion of individuals completing correct follow-up within 24 months of the letter. Multivariable logistic regression examined associations between odds of correct follow-up and individual and area-level characteristics. Results: Of the 7175 individuals who received a failsafe letter, 16.1% completed correct follow-up within 24 months. Individuals aged 70–74 had significantly lower odds of correct follow-up than those aged 60–64 (odd ratio (OR) = 0.59; 95% confidence interval (CI): 0.48–0.72). Living in areas with a higher proportion of young adults in higher education was associated with higher odds of correct follow-up (OR = 1.041; 95% CI: 1.002–1.080). Conclusions: The failsafe letter modestly improved follow-up among a hard-to-reach group. Older age and lower area-level educational attainment were linked to reduced odds of correct follow-up. Targeted efforts are needed to improve DC completion in these subgroups.