Determinants of colonoscopy adherence after positive colorectal cancer screening: Insights from individual and municipality-level data in Flanders.

[BACKGROUND] Timely follow-up colonoscopy after a positive fecal immunochemical test (FIT) is essential for the effectiveness of colorectal cancer (CRC) screening programs (CRC-SP). However, a substantial proportion of individuals fail to complete diagnostic follow-up. This study aimed to identify individual- and municipality-level factors associated with nonadherence to follow-up colonoscopy in the Flemish CRC-SP.

[METHODS] Individual-level data from the Flemish Centre for Cancer Detection (CCD), including 26,539 individuals with a positive FIT result in 2019, were linked with publicly available municipality-level indicators to assess demographic, socioeconomic, and healthcare-related characteristics. The outcome was nonadherence to follow-up colonoscopy within one year after a positive FIT result. A multivariable logistic regression model was developed using a structured approach: univariable screening (p < 0.15), multicollinearity assessment, and variable selection using least absolute shrinkage and selection operator (LASSO) regression. A random intercept for province was incorporated to account for potential clustering.

[RESULTS] A total of 5021 individuals (18.9 %) did not complete a follow-up colonoscopy within one year after a positive FIT result. In the final multivariable model, older age (65-69: OR = 1.12, 95 % CI: 1.03-1.21, p = 0.006; 70-74: OR = 1.29, 95 % CI: 1.20-1.40, p < 0.001), male gender (OR = 1.14, 95 % CI: 1.07-1.22, p < 0.001), and higher proportions of individuals living alone (OR = 1.02, 95 % CI: 1.00-1.03, p = 0.009) was associated with increased odds of nonadherence. In contrast, having a global medical dossier (GMD) were associated with better adherence (OR = 0.97, 95 % CI = 0.96-0.98, p < 0.001). Variance at the provincial level was negligible.

[CONCLUSIONS] This study provides evidence to support targeted implementation strategies within the Flemish CRC-SP. Strengthening primary care involvement and addressing social determinants of health may improve follow-up colonoscopy rates and enhance the equity and effectiveness of the screening program.