Establishment and Evaluation of a Nomogram Predicting Risks of Missed Diagnoses of Colorectal Polyps

Background: A missed diagnosis of colorectal polyps during colonoscopy may result in an interval colorectal cancer. The risk factors for a missed diagnosis or a method to predict the risk of a missed diagnosis of colorectal polyps during colonoscopy remain unidentified. Methods: : The clinical data of patients who underwent two colonoscopies within 3 months at the Affiliated Hospital of North Sichuan Medical College between February 2017 and August 2019 were retrospectively reviewed. Independent risk factors for missed diagnoses were identified and a nomogram was established for predicting the risk of missed diagnoses. Prediction performance of the nomogram was evaluated using C-index and calibration curves, and its clinical application value was evaluated using the Youden index and decision curve analysis. Results: : Independent influencing factors for missed diagnoses included age, endoscopist experience, bowel preparation, retroflected view, withdrawal time, number of polyps in the right colon, and number of polyps ≥6 mm. The C-index of the nomogram in the training and validation cohorts was 0.763 (95% confidence interval [ CI ]: 0.724-0.807) and 0.726 (95% CI 0.657-0.794), respectively. The optimal cut-off value of the nomogram calculated using the Youden index was 152.2 points. Under the cut-off value, the sensitivity, specificity, positive predictive value, and negative predictive value were 67.1%, 75.7%, 45.8%, and 88.2%, respectively, in the training cohort, and 57.1%, 79.9%, 53.3%, and 82.3%, respectively, in the validation cohort. Conclusions: : The nomogram provides a reference value for clinicians to analyse the risk of a missed diagnosis of colorectal polyps in individuals, identify high-risk groups, and formulate appropriate follow-up strategies.