The project aims to investigate whether colorectal cancer screening can be improved using blood tests, thereby reducing the number of unnecessary colonoscopies. The Danish colorectal cancer screening program was implemented in 2014, and currently, all individuals aged 50-74 are invited every two years to participate. Those who test positive for hidden blood in their stool are referred for a colonoscopy. More than a third of the approximately 25,000 colonoscopies performed annually in the screening program can be classified as unnecessary, as they reveal a normal colon. This results in avoidable and unpleasant procedures for individuals and strains healthcare resources.

The project seeks to reduce the number of these unnecessary colonoscopies by investigating whether blood biomarkers can identify individuals at very low risk of colorectal cancer after a positive stool test for hidden blood. By utilizing blood tests, screening could become more personalized, precise, and resource-efficient for the healthcare system.

Inclusion Criteria:

• Participation in the colorectal cancer screening program.

Exclusion Criteria:

• Participants are excluded if a colonoscopy is not completed unless this is due to a colorectal cancer obstruction.

All citizens referred to a colonoscopy at Vejle Hospital or Hospital Sønderjylland in the colorectal cancer screening program.