Development and validation of a nomogram for estimation of inadequate bowel preparation before colonoscopy in adults: an observational study

Background Adequate bowel preparation rate is not satisfactory at present. External verification for inadequate bowel preparation is needed. Methods A total of 1,216 patients undergoing colonoscopy in a tertiary hospital in China were included. Inadequate bowel preparation was defined by the Boston Bowel Preparation Scale. 13 risk factors were included into consideration. A logistic regression model derived from the derivation cohort was used to develop the nomogram. Measures of discrimination and calibration were determined in the internal and external validation cohorts separately. Decision curve analyses (DCA) was also used for assessing the clinical efficacy. Results There was a total of 224 patients with inadequate bowel preparation (24.5%) in the derivation cohort. Only 5 risk factors were considered in the final model, including hospitalization, diabetes, constipation, history of colonoscopy and indication for colonoscopy. The model had high levels of discrimination (the areas under the receiver operating characteristic curves, AUC = 0.76) and excellent calibration in both cohorts. The Hosmer–Lemeshow test showed no statistical significance, and DCA performed preferable net benefit in the nomogram. Conclusion An updated inadequate bowel preparation nomogram was well developed and validated. The new model can help doctors easily identify those at most risk of inadequate bowel preparation. Trial registration: Clinical Trials.gov, NCT04290715. Registered on February 25, 2020.