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Background Successful stone retrieval during endoscopic retrograde cholangiopancreatography (ERCP) in patients with radiologically confirmed choledocholithiasis may be influenced by pre-procedural imaging modality, interval timing of the procedure, stone size and alkaline phosphatase (ALP). The importance of these factors, however, has not been clearly defined in published studies.Objective To determine whether imaging modality, imaging-to-ERCP interval, stone diameter and ALP predict positive detection of choledocholithiasis during ERCP.Design This 3-year retrospective cohort study included 381 patients who underwent ERCP following radiological confirmation of choledocholithiasis. Data were collected on reported stone diameter, imaging modality, ALP (pre-procedural±four weeks and at time of procedure) and imaging to ERCP interval. Multivariate logistic regression was used to assess the influence of statistically significant variables on the primary outcome.Results Stones were detected in 82% of patients. In univariate analysis, higher ALP at imaging (p=0.003), ALP at procedure (p=0.008) and larger stone diameter (9.8 mm vs 6.3 mm, p<0.001) were significantly associated with positive ERCP findings. Multivariate analysis was performed using these variables, which identified only stone diameter as an independent predictor (OR 1.18; 95% CI 1.08 to 1.29; p<0.001).Conclusion In patients with radiologically confirmed choledocholithiasis, bile duct stone diameter, typically above 6.3 mm, is the strongest independent predictor of stone detection at ERCP. ALP levels were significant in univariate analysis; however, only stone size retained predictive value in multivariate modelling. These findings support using stone size to prioritise procedures and the development of predictive triage tools.