Abstract: Objective  To explore the miss rate of colorectal polyps and the relevant factors in back-to-back high-quality colonoscopy. Methods  Under the premise of limiting withdrawal time, intestinal preparation and successful rate of appendix intubation, patients were given a second colonoscopy after conventional colonoscopy. Size (diameter), location, shape and pathological type of colorectal polyps were recorded. Results   of the two tests were collected to calculate the misdiagnosis rate of colon polyps. The relationship between the obtained data and relevant factors was analyzed.  Results  A total of 462 polyps were found in 164 patients by continuous colonoscopy, the total miss rate being 17.7%. There was obvious correlation between miss rate and size (χ2=25.055, P<0.001), location (χ2=15.134, P=0.010) and shape (χ2=22.901, P<0.001) of polyps. Multi-factor statistical analysis of the relevant factors showed that polyp size was the protective factor of missed diagnosis. The larger the polyp was, the smaller the miss rate was. Compared with polyps with diameter ≤5mm, polyps with diameter 6~10mm had (OR: 0.38, 95%CI: 0.22-0.65), and polyps with diameter >10mm had (OR: 0.10, 95%CI: 0.02-0.43). Compared with the rectum, sigmoid colon, transverse colon and ascending colon had significantly increased miss rate. The miss rate was markedly higher in sessile polyps (OR: 4.77, 95%CI: 2.34-9.72) than in pedunculated polyps. The pathological type was not correlated to miss rate. Conclusion  Patients with colorectal polyps risk a certain degree of miss rate during continuous colonoscopy. Miss rate is associated with size, location, and shape but not with the pathological type of polyps.

Key words: Colonoscopy, Miss rate, Colorectal polyps