Abstract:【Abstract】Objectives Autoimmune gastritis (AIG) is a chronic and progressive damage to gastric corpus and fundus mucosa caused by autoimmune mediated inflammation. Endoscopy is an important opportunity to discover and diagnose AIG. However, there is often a substantial diagnostic delay in clinical practice. The aim of this study was to characterize the endoscopic appearances of AIG, and develop an endoscopy-based model for AIG (EBM-AIG) diagnosis. Methods A total of 448 patients diagnosed with chronic gastritis were retrospectively enrolled from two tertiary hospitals in China between January 2022 and November 2023. They were randomly divided into a derivation cohort (n=302) and a validation cohort (n=146) at a ratio of 2:1. In the derivation cohort, endoscopic features were evaluated and an EBM-AIG scoring model was developed using multivariate logistic regression analysis, with points assigned based on the regression coefficients. The diagnostic performance of the model was assessed using receiver operating characteristic (ROC) curve analysis and validated in the validation cohort. Results Reverse atrophy (OR 42.59; 95% CI 41.66-43.52), sticky adherent dense mucus (OR14.25; 95% CI 13.47-15.03), remnant oxyntic mucosa (OR 4.63; 95% CI 3.57-5.69) and diffuse reddened and edematous gastric fundus gland mucosa (OR 21.52; 95% CI 20.72-22.32) were significantly associated with AIG. An EBM-AIG scoring model (total score 0-10) was constructed based on these four features. In the derivation cohort, the model showed excellent discrimination with an area under the ROC curve (AUC) of 0.985. Using a cut-off score of ≥5, the diagnostic accuracy, sensitivity, and specificity were 95.4%, 92.6%, and 97.2%, respectively. In the validation cohort, the EBM-AIG score showed good diagnostic ability of AIG with the AUROC 0.994 (95%CI 0.983-1.000). Conclusions The EBM-AIG scoring model, based on the four endoscopic features of reverse atrophy, sticky mucus, remnant oxyntic mucosa, and diffuse reddened and edematous gastric fundus gland mucosa, demonstrated excellent diagnostic performance for AIG in internal validation. A score of ≥5 holds high diagnostic value and can serve as a practical tool for endoscopically suggesting AIG, guiding targeted biopsies for pathological confirmation.