This ambispective observational study aims to validate the Odesa Criteria 2026 (OC26), a flexible domain-based point scoring system for diagnosing autoimmune pancreatitis. The study evaluates diagnostic accuracy and reproducibility of OC26 across clinical, serological, morphological, and histological domains.

The study uses an ambispective design, including both retrospective and prospective data collection.

Autoimmune pancreatitis (AIP) remains a diagnostic challenge due to its heterogeneous clinical presentation and overlap with pancreatic cancer and other inflammatory conditions. The Odesa Criteria 2026 (OC26) were developed as a flexible, domain-based point scoring system integrating four diagnostic domains: morphology, serology, clinical features, and histology. Each domain contributes weighted points toward a total diagnostic score, enabling structured and reproducible assessment across diverse patient phenotypes.

This ambispective observational study evaluates the diagnostic performance of OC26 in real-world clinical practice. The study assesses sensitivity, specificity, predictive values, likelihood ratios, and overall diagnostic accuracy using final clinical diagnosis as the reference standard. Additional analyses include interobserver agreement for domain scoring, diagnostic performance of individual domains, ROC curve analysis for the total OC26 score, and determination of the optimal diagnostic cut-off.

The study aims to validate OC26 as a practical, scalable, and reproducible diagnostic tool for autoimmune pancreatitis, supporting its implementation in routine clinical workflows and future international guideline development.

Inclusion Criteria:

• Adults (≥18 years) undergoing evaluation for suspected autoimmune pancreatitis.
• Availability of clinical, serological, imaging, and/or histological data required for OC26 scoring.
• Ability to provide informed consent (for prospective participants).

Exclusion Criteria:

• Confirmed alternative diagnosis explaining pancreatic findings (e.g., pancreatic cancer, acute pancreatitis of other etiology).
• Incomplete diagnostic data preventing OC26 scoring.
• Prior pancreatic surgery altering diagnostic interpretation.

Patients undergoing diagnostic evaluation for suspected autoimmune pancreatitis at a tertiary referral center. The study includes both retrospective cases with complete diagnostic data and prospective participants evaluated according to the Odesa Criteria 2026 (OC26).

Individual participant data will not be shared because the study involves sensitive clinical information and the dataset is not intended for external distribution. Only aggregated, de-identified results will be available in publications.