Prospective cohort studies, in which total colonoscopy was used to screen for polyps and colorectal cancer in asymptomatic adults were eligible for inclusion. Asymptomatic people were defined as those aged 40 to 75 years, without symptoms of abdominal pain, rectal bleeding or change in bowel habit. Included studies were required to have a minimum of 500 participants and to report diagnostic yield for adenoma (or advanced adenoma) and colorectal cancer. Advanced adenoma was defined as size 10mm or greater, or containing villous histology, or with high grade dysplasia. Complication rates were also an outcome of interest.
Studies of other screening methods and studies, where colonoscopy was performed as a second line examination of symptomatic patients or for post-treatment follow-up, were excluded.
Where reported, the mean age of study participants ranged from 44.8 to 62.9 years and four out of ten studies recorded the inclusion of high-risk (previous family history) participants..
The authors did not state how studies were selected for the review, or how many reviewers performed the selection.