Adherence to colorectal cancer screening: four rounds of faecal immunochemical test-based screening

The effectiveness of faecal immunochemical test (FIT)-based screening programs is highly dependent on consistent participation over multiple rounds. We evaluated adherence to FIT screening over four rounds and aimed to identify determinants of participation behaviour. A total of 23 339 randomly selected asymptomatic persons aged 50-74 years were invited for biennial FIT-based colorectal cancer screening between 2006 and 2014. All were invited for every consecutive round, except for those who had moved out of the area, passed the upper age limit, or had tested positive in a previous screening round. A reminder letter was sent to non-responders. We calculated participation rates per round, response rates to a reminder letter, and differences in participation between subgroups defined by age, sex, and socioeconomic status (SES). Over the four rounds, participation rates increased significantly, from 60% (95% CI 60-61), 60% (95% CI 59-60), 62% (95% CI 61-63) to 63% (95% CI 62-64; P for trend <0.001) with significantly higher participation rates in women in all rounds (P