2022 ACR/EULAR classification criteria for microscopic polyangiitis. Includes positive and negative weighted items to distinguish MPA from GPA, EGPA, and other vasculitides. Score ≥5 classifies as MPA.
≥5Score threshold
91.0%Sensitivity
94.0%Specificity
2022Published
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Entry Requirement
Required before applying these criteria
These criteria apply to patients with an established diagnosis of small or medium vessel vasculitis, nephritis, or pulmonary hemorrhage. They classify the vasculitis subtype, not whether vasculitis is present. MPA is ANCA-associated vasculitis without granulomas - if granulomas are present on biopsy, consider GPA.
Vasculitis diagnosis required before scoring
+
Positive Criteria - Add Points
Laboratory features
Serologic findings most characteristic of MPA.
Pulmonary features
Lung involvement characteristic of MPA, particularly fibrosis.
Histopathology
Biopsy findings supporting MPA.
-
Negative Criteria - Subtract Points
Features that reduce the MPA score
These findings are more characteristic of GPA than MPA. When present, they subtract from the total score. Check any that apply to this patient.
Classification Score
0
Total Score (threshold ≥5)
-80512
Entry Required
Confirm vasculitis diagnosis before scoring.
Criteria Breakdown
MPO-ANCA / p-ANCA positive+6
Pulmonary fibrosis / ILD+3
Pauci-immune GN on biopsy+3
PR3-ANCA / c-ANCA positive-1
Nasal polyps-1
Granuloma on biopsy-3
Eosinophilia ≥1x10&sup9;/L-4
2022 ACR/EULAR classification criteria are for research classification, not clinical diagnosis. Requires prior diagnosis of vasculitis. Consult a rheumatologist for management decisions.
Frequently Asked Questions
Microscopic polyangiitis (MPA) is a necrotizing small-vessel vasculitis that is pauci-immune (few or no immune complex deposits) and non-granulomatous. It most commonly causes pauci-immune glomerulonephritis - a leading cause of rapidly progressive GN - and pulmonary capillaritis resulting in diffuse alveolar hemorrhage. Unlike GPA, MPA does not involve the upper respiratory tract with granulomatous inflammation, nasal cartilage destruction, or subglottic stenosis. MPA is part of the ANCA-associated vasculitis (AAV) family and is most commonly associated with MPO-ANCA (p-ANCA), though PR3-ANCA can occur.
MPO-ANCA (anti-myeloperoxidase antibodies, producing p-ANCA on IIF) is positive in approximately 70-80% of MPA patients and is strongly associated with MPA over GPA. The high weight (+6) reflects both its sensitivity for MPA and its specificity relative to GPA. A patient with MPO-ANCA alone nearly reaches the classification threshold of 5 points, reflecting the biological and diagnostic centrality of this antibody. In contrast, PR3-ANCA is more strongly associated with GPA and subtracts 1 point from the MPA score. The differential ANCA weighting is the main mechanism by which the 2022 criteria distinguish GPA from MPA.
MPA - particularly MPO-ANCA-associated disease - has a well-established association with interstitial lung disease (ILD), most commonly with a usual interstitial pneumonia (UIP) or non-specific interstitial pneumonia (NSIP) pattern on HRCT. The mechanism likely involves repeated subclinical alveolar inflammation from MPO-ANCA-activated neutrophils, leading to progressive fibrosis. Importantly, ILD may precede the clinical diagnosis of MPA by months to years. In patients with UIP-pattern ILD being evaluated for idiopathic pulmonary fibrosis (IPF), MPO-ANCA testing should be considered, as MPO-ANCA-associated ILD may respond to immunosuppressive therapy unlike true IPF.
Both MPA and GPA can cause pauci-immune GN, pulmonary capillaritis, and are ANCA-associated. The key distinguishing features are: (1) ANCA type - MPO-ANCA favors MPA (+6), PR3-ANCA favors GPA (+5 for GPA, -1 for MPA); (2) Granulomas - present in GPA (+2 for GPA), absent in MPA (-3 if present); (3) Upper respiratory tract - nasal cartilage destruction and subglottic stenosis are GPA features (+2 to +3 for GPA); (4) Pulmonary fibrosis/ILD - far more common in MPA (+3). The 2022 criteria deliberately use positive and negative items so that features of one diagnosis subtract from the score of the other, improving specificity.
Significant eosinophilia (blood eosinophils ≥1x10&sup9;/L) is a defining feature of eosinophilic granulomatosis with polyangiitis (EGPA, formerly Churg-Strauss syndrome), not MPA. The -4 weight is the largest negative item because marked eosinophilia essentially rules out MPA and should prompt consideration of EGPA, particularly in patients with concurrent asthma, nasal polyps, or high IgE. Mild eosinophilia (<1x10&sup9;/L) can occur in any AAV and is not penalized. The threshold of 1x10&sup9;/L was chosen to specifically capture the marked eosinophilia characteristic of EGPA.
Pauci-immune glomerulonephritis is the most common renal manifestation of all AAV and is a medical emergency. It typically presents as rapidly progressive GN (RPGN) with acute kidney injury, hematuria (dysmorphic RBCs, RBC casts), and proteinuria. Without prompt treatment, it can lead to end-stage renal disease within weeks. On biopsy, it shows focal segmental necrotizing lesions and cellular crescents with little or no immunofluorescence staining. Treatment with rituximab or cyclophosphamide combined with high-dose glucocorticoids is the standard of care. Plasma exchange may be added in severe cases with dialysis dependence, though its benefit is debated based on the PEXIVAS trial.
In the 2022 ACR/EULAR validation study, the MPA criteria (score ≥5) demonstrated sensitivity of 91.0% and specificity of 94.0% against other vasculitides. These criteria replaced the older approach of diagnosing MPA by exclusion (i.e., AAV without GPA or EGPA features). The 2022 criteria were developed alongside criteria for GPA and EGPA as part of a coordinated project, allowing the three AAV subtypes to be formally distinguished from each other using a single classification framework with shared positive and negative items.