From the Guidelines
For suspected ANCA vasculitis, I recommend ordering both ANCA serologies and supporting laboratory tests, starting with ANCA testing including anti-proteinase 3 (PR3-ANCA) and anti-myeloperoxidase (MPO-ANCA) antibodies by immunofluorescence and ELISA methods, as recommended by the 2024 EULAR guidelines 1.
Laboratory Tests for ANCA Vasculitis
The following laboratory tests are recommended:
- ANCA testing including anti-proteinase 3 (PR3-ANCA) and anti-myeloperoxidase (MPO-ANCA) antibodies by immunofluorescence and ELISA methods
- Comprehensive metabolic panel (CMP)
- Complete blood count (CBC) with differential
- Erythrocyte sedimentation rate (ESR)
- C-reactive protein (CRP)
- Urinalysis with microscopy
- Urine protein-to-creatinine ratio
- Complement levels (C3, C4)
- Anti-glomerular basement membrane (anti-GBM) antibodies
- Rheumatoid factor
- Antinuclear antibodies (ANA)
Rationale
These tests help establish diagnosis, assess organ involvement, and monitor disease activity, though definitive diagnosis often requires tissue biopsy from affected organs. The 2024 EULAR guidelines recommend testing for both PR3-ANCA and MPO-ANCA using a high-quality antigen-specific assay as the primary method of testing 1. The KDIGO 2024 clinical practice guideline also recommends the use of high-quality antigen-specific immunoassays for MPO- and PR3-ANCA testing 1.
Additional Considerations
If pulmonary involvement is suspected, chest imaging should be included. PR3-ANCA is typically associated with granulomatosis with polyangiitis (formerly Wegener's), while MPO-ANCA is more common in microscopic polyangiitis and eosinophilic granulomatosis with polyangiitis. A positive biopsy is strongly supportive of a diagnosis of vasculitis, and biopsies should be performed to assist in establishing a new diagnosis of AAV and for further evaluation of patients suspected of having relapsing vasculitis 1.
From the Research
Laboratory Tests for Suspected ANCA Vasculitis
The following laboratory tests are ordered for suspected Anti-Neutrophil Cytoplasmic Antibody (ANCA) vasculitis:
- Indirect immunofluorescence (IIF) test to screen for ANCA 2, 3, 4, 5
- Antigen-specific enzyme-linked immunosorbent assays (ELISAs) for proteinase 3 (PR3) and myeloperoxidase (MPO) to confirm IIF-positive sera 2, 3, 4, 5
- PR3-ANCA and MPO-ANCA immunoassays, which can be used without the need for IIF in some cases 5
Testing Strategies
Different testing strategies may be employed depending on the clinical context:
- For new-onset vasculitis, sera should be examined for both PR3- and MPO-ANCA using highly sensitive and specific assays 2
- For treated vasculitis or non-vasculitic disease, IIF screening followed by confirmation of IIF-positive sera in antigen-specific assays may be used 2
- In some cases, a "gating policy" based on clinical information may be used to guide testing and avoid misdiagnosis 5
Interpretation of Results
The interpretation of ANCA test results should be done in the context of clinical information: