Appropriate Workup for Suspected Vasculitis
The appropriate workup for suspected vasculitis should include complete blood count with differential, comprehensive metabolic panel, inflammatory markers (ESR, CRP), urinalysis with microscopy, ANCA testing (both MPO-ANCA and PR3-ANCA), and tissue biopsy of affected organs, with imaging selected based on suspected vessel size involvement. 1
Initial Laboratory Evaluation
- Complete blood count with differential: Look for anemia, leukocytosis, eosinophilia (especially in Churg-Strauss syndrome)
- Comprehensive metabolic panel: Assess renal and liver function
- Inflammatory markers:
- Erythrocyte sedimentation rate (ESR)
- C-reactive protein (CRP)
- Urinalysis with microscopic examination: Essential to detect hematuria, proteinuria, and red cell casts suggesting renal involvement
- Serological testing:
- PR3-ANCA and MPO-ANCA using high-quality antigen-specific assays
- If immunoassay is negative but clinical suspicion remains high, perform a second test (another immunoassay and/or immunofluorescence) 1
- Complement levels (C3, C4) to help differentiate types of vasculitis
- Hepatitis B and C testing, particularly with liver involvement or risk factors 2
Tissue Biopsy
Tissue biopsy is the gold standard for diagnosis with a diagnostic yield of over 70% 1:
- Target clinically affected tissue for highest diagnostic yield
- For giant cell arteritis, perform temporal artery biopsy (minimum 1 cm length)
- For cutaneous vasculitis, biopsy should extend to the subcutis from the most tender, reddish, or purpuric lesional skin 3
- Consider concomitant biopsy for direct immunofluorescence to distinguish IgA-associated vasculitis (Henoch-Schönlein purpura) from IgG/IgM-associated vasculitis 3
Imaging Studies
Select imaging based on suspected vessel size involvement 1:
| Vessel Size | Recommended Imaging |
|---|---|
| Large | CT/CTA, MRI/MRA, or FDG-PET/CT |
| Medium | CTA of affected regions (renal, mesenteric, coronary) |
| Small | MRI/MRA or FDG-PET/CT |
Disease Classification and Assessment
- Classify disease according to ANCA serotype (PR3-ANCA, MPO-ANCA, or ANCA-negative) 1
- Use Chapel Hill Consensus Conference definitions and ACR classification criteria
- Categorize by vessel size affected:
- Large vessels: Takayasu arteritis, giant cell arteritis
- Medium and small muscular arteries: Polyarteritis nodosa, Churg-Strauss syndrome, Wegener's granulomatosis
- Small vessels: Hypersensitivity vasculitis, Henoch-Schönlein purpura, microscopic polyangiitis, cryoglobulinemia 4
Important Considerations
- A negative ANCA does not exclude AAV diagnosis, especially in disease limited to respiratory tract or renal-limited vasculitis 1
- Treatment should not be delayed while waiting for biopsy results in ANCA-positive patients with compatible clinical presentation, especially in rapidly deteriorating patients 1
- Patients with suspected primary small and medium vessel vasculitis should be managed in collaboration with, or at centers of expertise 1
Disease Activity Assessment
For comprehensive disease assessment, include:
- Birmingham Vasculitis Activity Score
- Disease Extent Index
- Vasculitis Damage Index
- Functional assessment (Short Form 36) 1
This structured approach to vasculitis workup ensures thorough evaluation of suspected cases, enabling accurate diagnosis and timely initiation of appropriate treatment to improve morbidity and mortality outcomes.