Evaluation of ACR/EULAR 2022 ANCA associated vasculitis classification criteria: The impact of reclassification in a large cohort with long-term follow-up

Objective: To compare the performance of the EMA (European Medicines Agency) algorithm for classification of necrotizing vasculitis and the new American College of Rheumatology (ACR)/European League of Rheumatology (EULAR) 2022 classification criteria in our single center long-term anti-neutrophil cytoplasmic antibody (ANCA) associated vasculitis (AAV) cohort. Methods: Patients classified as granulomatosis with polyangiitis (GPA) and microscopic polyangiitis (MPA) according to EMA algorithm were included into the study. ACR/EULAR 2022 classification criteria were implemented retrospectively. Antibody-based classification (ABC) was performed as a third model, which classify patients either GPA or MPA if anti-proteinase 3 (PR3) or myeloperoxidase (MPO) is positive, respectively. Kappa analysis was used to explore the agreement between criteria sets. Results: Data of 221 patients classified as GPA (85.6%) and MPA (14.5%) according to EMA algorithm were included. PR3-ANCA and MPO-ANCA was positive in 124 (56.1%) and 79 (35.7%) patients. ACR/EULAR 2022 classified 137 (62%) and 84 (38%) patients as GPA and MPA, respectively. Nine (4%) patients were classified as both GPA and MPA, nine (4%) patients were unclassifiable. The new criteria set was in weak agreement with EMA algorithm (kappa=0.28 for GPA and 0.24 for MPA). On the other hand, strong agreement with ABC was observed (kappa=0.88 for GPA and 0.89 for MPA). Conclusion: A significant number of patients who classified as GPA could be classified as MPA with the ACR/EULAR 2022 criteria and agreement with EMA algorithm was weak. The new criteria set was indecisive for some AAV patients. Strong agreement with ABC indicated the significant influence of serology in the ACR/EULAR 2022 criteria.