Risk factors of missed colorectal lesions after colonoscopy.

Several studies have reported a significant rate of missed colorectal polyps during colonoscopy. This study aimed to determine the variables that affect the miss rate of colorectal polyps.We performed a retrospective observational study of patients who, between January 2007 and December 2014, had undergone a second colonoscopy within 6 months of their first. In all patients, the first colonoscopy constituted a screening or surveillance colonoscopy as part of a health check-up, and the patients were referred to the endoscopic clinic if there were meaningful polyps. The miss rate of colorectal polyps was evaluated, as were the variables related to these missed lesions.Among 659 patients (535 men), the miss rate of colorectal polyps was 17.24% (372/2158 polyps), and 38.69% of patients (255/659 patients) had at least 1 missed polyp. The most common site for missed polyps was the ascending colon (29.8%), followed by the sigmoid colon (27.8%). The miss rate of polyps was higher in men [odds ratio (OR) = 1.611, 95% confidence interval (95% CI) = 1.024-2.536], patients with multiple polyps at their first colonoscopy (OR = 1.463, 95% CI = 0.992-2.157), and patients who had a history of polyps (OR = 23.783, 95% CI = 3.079-183.694). Multiple missed polyps were more frequently located in the right colon (OR = 2.605, 95% CI = 1.458-4.657), and the risk of sessile serrated adenoma/polyp was greater in the right colon (OR = 10.418, 95% CI = 2.073-52.353).Endoscopists should pay careful attention in patients who have multiple polyps and in those who have a history of polyps, because such patients are at a high risk of missed polyps in colonoscopy.