Novel indicator for colonoscopy insertion difficulty and its application in predictive modelling: a multicentre prospective study protocol in China.

backgroundColonoscopy is a cornerstone for the screening and diagnosis of colorectal diseases. Colonoscopy insertion difficulty is associated with examination quality, procedural efficiency and patient comfort. Cecal intubation time (CIT) is commonly used as a surrogate measure of insertion difficulty; however, it is substantially influenced by endoscopist experience, equipment characteristics and institutional factors, limiting its objectivity and comparability. This study will develop and validate a standardised colonoscopy insertion time (SCIT) metric that better reflects patient-related procedural difficulty while minimising non-patient-related variability. Additionally, we will identify factors associated with insertion difficulty and develop predictive models using machine learning techniques. METHODS AND ANALYSIS: This multicentre prospective observational study will enrol approximately 3000 adults undergoing sedated colonoscopy across one primary centre and five participating centres. CIT will be prospectively recorded and analysed in relation to patient characteristics, endoscopist experience, colonoscope type and study centre. Three standardisation approaches, including Z-score standardisation, median-based standardisation and min-max normalisation, will be applied to generate SCIT. The primary outcome will be SCIT, and the optimal standardisation method will be selected based on its ability to reduce variability attributable to operator-related, equipment-related and centre-related factors while preserving clinically meaningful associations with patient characteristics. Mixed-effects models will be used to account for clustering by endoscopist and study centre. Based on the selected SCIT metric, machine learning models will be developed using preprocedural clinical variables to predict insertion difficulty. Model performance will be evaluated using measures of discrimination, calibration and predictive accuracy. ETHICS AND DISSEMINATION: The study received initial ethical approval from the Ethics Committee of the Second Hospital of Jilin University (Approval No. 2024-467-1) on 4 November 2024. Subsequent protocol amendments were approved on 25 March 2026. All participants will provide written informed consent prior to enrolment. Patient privacy and data confidentiality will be strictly maintained. The results will be disseminated through SCI-indexed journals and presentations at national and international academic conferences to inform future research and clinical practice related to colonoscopy performance evaluation. TRIAL REGISTRATION NUMBER: NCT07228715.