Evaluation of the ACR/EULAR 2022 criteria for classification of ANCA-associated vasculitis in a population-based cohort from Sweden.

OBJECTIVE:To evaluate the ACR/EULAR 2022 criteria for AAV classification and compare it to the EMA algorithm and to classification based only on ANCA serology. METHODS:In the analysis, 374 cases (47% female) were classified according to EMA algorithm, ANCA serology, and ACR/EULAR criteria. The agreement rate was calculated using the kappa (κ) statistic. RESULTS:Under EMA, 192 patients were classified as GPA, 159 as MPA, and 23 as EGPA. The ACR/EULAR criteria classified 199 patients as GPA, 136 as MPA, and 22 as EGPA. Four patients (1.1%) met criteria of two disease categories, and thirteen (3.5%) were unclassifiable. The observed agreement between EMA and ACR/EULAR was 85% for GPA, 75% for MPA, and 96% for EGPA. The unweighted κ statistic was 0.66 (95% CI 0.60-0.74). Of the 188 PR3-ANCA-positive patients, 186 (98.9%) were classified as GPA using ACR/EULAR criteria, and 135 of 161 (83.8%) MPO-ANCA-positive patients were classified as MPA. With a classification solely based on ANCA-specificity, agreement with ACR/EULAR was 99% for GPA and 88% for MPA. CONCLUSIONS:EMA and ACR/EULAR classification give similar results. A small proportion of patients cannot be classified or fall into two categories. Some patients exhibiting granuloma, a key feature of GPA, are nevertheless classified as MPA, conflicting with the current view of histopathology of AAV. There is high agreement of ANCA-based classification with that of ACR/EULAR, reflected in the considerable weight granted to ANCA in the new criteria. These crucial elements within the new criteria necessitate a consensus discussion among field experts.