What are the diagnostic tests for vasculitis?

Diagnostic Tests for Vasculitis

The primary diagnostic tests for vasculitis include ANCA testing (specifically MPO and PR3 immunoassays), tissue biopsy, and appropriate laboratory and imaging studies based on suspected vessel involvement. 1

Primary Diagnostic Approach

ANCA Testing

• High-quality antigen-specific immunoassays for MPO-ANCA and PR3-ANCA are the preferred screening method for ANCA-associated vasculitis (AAV) 1
• About 90% of patients with small-vessel vasculitis or necrotizing crescentic glomerulonephritis have ANCA directed primarily against MPO or PR3 1
• ANCA testing should include both:
  • Indirect immunofluorescence to detect labeling pattern (cytoplasmic or perinuclear)
  • ELISA for specific antigens (MPO and PR3) 1

Tissue Biopsy

• Biopsy remains the gold standard for diagnosing vasculitis 1
• Diagnostic yield of biopsies showing granuloma or vasculitis is over 70% 1
• Kidney biopsy yield in granulomatosis with polyangiitis can be as high as 91.5% 1
• Biopsy should be performed from the most affected tissue when accessible 2
• For cutaneous vasculitis, biopsy should extend to subcutis from the most tender, reddish, or purpuric lesional skin 2

Additional Laboratory Tests

Essential Laboratory Workup

• Complete blood count with differential
• Erythrocyte sedimentation rate (ESR) and C-reactive protein (CRP)
• Serum creatinine and comprehensive biochemistry profile
• Urinalysis (looking for hematuria, red cell casts, proteinuria)
• Complement levels (C3 and C4)
• Immunoglobulin levels 3, 4

Specialized Testing Based on Clinical Presentation

• Anti-glomerular basement membrane (anti-GBM) antibodies for suspected Goodpasture's syndrome 1, 4
• Hepatitis B and C serology (especially with liver involvement) 3, 5
• Cryoglobulins 4
• Anti-C1q antibodies for immune complex-associated small-vessel vasculitis 4

Imaging Studies

• MRI with ADC maps, diffusion, and gradient echo sequences is the investigation of choice for cerebral vasculitis 6
• Angiography for medium and large vessel vasculitis 3
• Ultrasound of temporal artery for suspected giant cell arteritis (88% sensitive, 97% specific) 1

Structured Clinical Assessment

• A structured clinical assessment should be conducted at each visit to detect organ involvement 1
• For suspected temporal arteritis, temporal artery biopsy should be performed but should not delay treatment 1

Common Pitfalls and Caveats

1. ANCA-negative vasculitis: About 10% of patients with AAV are ANCA-negative; absence of ANCA does not exclude the diagnosis 1

2. Treatment before biopsy: In cases with high clinical suspicion and positive ANCA serology, treatment should not be delayed while waiting for biopsy results, especially in rapidly deteriorating patients 1

3. Differential diagnosis: Several non-vasculitic diseases may mimic vasculitis, including systemic lupus erythematosus, infections, and malignancies 1

4. Referral to expertise: Patients with suspected vasculitis should be managed in collaboration with or at centers of expertise due to the complexity of diagnosis and management 1

5. Biopsy timing: If treatment with glucocorticoids is started before biopsy, the biopsy should not be delayed beyond 1-2 weeks of commencing therapy 1

By following this diagnostic approach, clinicians can efficiently diagnose and classify vasculitis, allowing for timely initiation of appropriate treatment to improve morbidity, mortality, and quality of life outcomes.