Determinants of non-participation in colon examination following positive stool sample in colorectal cancer screening

Background: National screening for colorectal cancer was initiated in Denmark in 2014. All individuals with a positive stool sample at initial screening was invited for follow-up colon examination. Participation is registered in Danish Colorectal Cancer Screening Database. Methods: Invitations and registered colon examinations from 2014-15 from Danish Colorectal Cancer Screening Database (dates and region of residence). Linked with the Income Statistics Register (income year previous to invitation), the Populations's Education Register (highest achieved educational level previous year), the Danish Civil Registration System (gender, age and immigration status), the National Patient Register (previous colorectal cancer) and the Danish Register of Causes of Death (date of death). Logistic regression models estimated odds of non-participation in examination. Stratification used to control for interaction with sex. Results: Participation for follow-up was high at 89.0%. Social inequalities was found in subgroups of income quartiles, educational level, immigrations status, marital status and region of residence in males.Social inequalities was found in subgroups of income quartiles, marital status and region of residence in females. Lowest male participation proportion was in non-western immigrants (80,6%), singles (83,5%) lowest income quartile (84,2%). Lowest female participation proportion was in non-western immigrants (84,1%), residents of Capital Denmark Region (84,8%) and singles (85,0%). Highest male/female participation proportion was in those of the highest income quartile (m/f: 93,1%/91,5%). Adjusted odds ratios (OR) of non-participation was highest in residents of Capitol Denmark Region, compared to North Denmark Region, followed by non-western immigrants, compared to natives, and singles compared to those with a partner in both men and women. The lower participation proportions in the eastern regions was not caused by socioeconomic differences. Conclusions: Participation in follow-up colon examination in the Danish colorectal cancer screening is high compared to international programs. Large inequalities are present at follow-up screening examination, especially among men. Inequalities from intital screening(1) are enhanced at follow-up screening examination. The cancer screening program should be altered to target low participating subgroups and their possible barriers to colon examination.