Background Screening for life-threatening diseases has potential benefits and harms. In screening for colorectal cancer (CRC) some potential harms are the negative psychosocial consequences of being diagnosed with polyps or receiving a false-positive result.

In 2014 a national CRC screening programme was implemented in Denmark, using an immunochemical faecal occult blood test (iFOBT) as the screening method and targeting all citizens aged 50–74. In the implementation period of the screening programme (2014–2017) citizens were invited to participate in a randomised design. According to the latest Danish CRC screening report from 2016, the positive rate has been approximately 7%. All citizens with positive results were urged to have a colonoscopy where subsequently 63.5% had a clean colon or benign polyps, 31% had adenomatous polyps and 5.5% were diagnosed with CRC. Hence, thousands of healthy people have undergone a colonoscopy to confirm that they do not have CRC. Moreover, thousands of people were diagnosed with polyps: benign and adenomatous.

Previous studies investigating psychosocial consequences of CRC screening have shown diverging results. However, all these studies were performed using generic questionnaires, which have shown not to be adequate in measuring psychosocial consequences in a medical screening setting.

Objectives The objective of this study was to investigate psychosocial consequences of participating in a national colorectal cancer screening programme, with a condition-specific questionnaire specifically developed for measuring psychosocial consequences in a CRC screening setting.

Method The study was a longitudinal study with a randomised design. We performed data collection in the Region Zealand county of Denmark in the period of April 2017 – March 2018. We enrolled participants with a positive iFOBT consecutively and matched them on gender, municipality and year of birth in a 2:1 design with citizens with negative results, non-attenders and a control group randomised to screening in the last part of 2017. We sent a condition-specific questionnaire four days after the participants received their iFOBT result and again eight weeks after the final diagnosis. The primary outcome was psychosocial consequences measured by a condition-specific questionnaire.

Results Preliminary results and conclusions will be presented at the conference.