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Objective: To develop and validate new classification criteria for Takayasu arteritis (TAK). Methods: Patients with vasculitis or comparator diseases were recruited into an international cohort. The study proceeded in 6 phases: 1) identification of candidate criteria items, 2) collection of candidate items present at diagnosis, 3) expert panel review of cases, 4) data‐driven reduction of candidate items, 5) derivation of a points‐based classification score in a development data set, and 6) validation in an independent data set. Results: The development data set consisted of 316 cases of TAK and 323 comparators. The validation data set consisted of an additional 146 cases of TAK and 127 comparators. Age ≤60 years at diagnosis and imaging evidence of large‐vessel vasculitis were absolute requirements to classify a patient as having TAK. The final criteria items and weights were as follows: female sex (+1), angina (+2), limb claudication (+2), arterial bruit (+2), reduced upper extremity pulse (+2), reduced pulse or tenderness of a carotid artery (+2), blood pressure difference between arms of ≥20 mm Hg (+1), number of affected arterial territories (+1 to +3), paired artery involvement (+1), and abdominal aorta plus renal or mesenteric involvement (+3). A patient could be classified as having TAK with a cumulative score of ≥5 points. When these criteria were tested in the validation data set, the model area under the curve was 0.97 (95% confidence interval [95% CI] 0.94–0.99) with a sensitivity of 93.8% (95% CI 88.6–97.1%) and specificity of 99.2% (95% CI 96.7–100.0%). Conclusion: The 2022 American College of Rheumatology/EULAR classification criteria for TAK are now validated for use in research. [ABSTRACT FROM AUTHOR]

Objective: To develop and validate classification criteria for microscopic polyangiitis (MPA). Methods: Patients with vasculitis or comparator diseases were recruited into an international cohort. The study proceeded in 5 phases: 1) identification of candidate items using consensus methodology, 2) prospective collection of candidate items present at the time of diagnosis, 3) data‐driven reduction of the number of candidate items, 4) expert panel review of cases to define the reference diagnosis, and 5) derivation of a points‐based risk score for disease classification in a development set using least absolute shrinkage and selection operator logistic regression, with subsequent validation of performance characteristics in an independent set of cases and comparators. Results: The development set for MPA consisted of 149 cases of MPA and 408 comparators. The validation set consisted of an additional 142 cases of MPA and 414 comparators. From 91 candidate items, regression analysis identified 10 items for MPA, 6 of which were retained. The final criteria and their weights were as follows: perinuclear antineutrophil cytoplasmic antibody (ANCA) or anti–myeloperoxidase‐ANCA positivity (+6), pauci‐immune glomerulonephritis (+3), lung fibrosis or interstitial lung disease (+3), sino‐nasal symptoms or signs (−3), cytoplasmic ANCA or anti–proteinase 3 ANCA positivity (−1), and eosinophil count ≥1 × 109/liter (−4). After excluding mimics of vasculitis, a patient with a diagnosis of small‐ or medium‐vessel vasculitis could be classified as having MPA with a cumulative score of ≥5 points. When these criteria were tested in the validation data set, the sensitivity was 91% (95% confidence interval [95% CI] 85–95%) and the specificity was 94% (95% CI 92–96%). Conclusion: The 2022 American College of Rheumatology/European Alliance of Associations for Rheumatology classification criteria for MPA are now validated for use in clinical research. [ABSTRACT FROM AUTHOR]