What is the appropriate workup for a patient suspected of having vasculitis?

Workup for Suspected Vasculitis

For patients suspected of having vasculitis, a comprehensive diagnostic workup should include biopsy of affected tissue, ANCA testing with immunofluorescence and ELISA for PR3/MPO antibodies, laboratory studies, and appropriate imaging based on suspected vessel size involvement. 1

Initial Assessment and Classification

• Disease Classification: Categorize based on vessel size and clinical presentation:

  • Large vessel: Takayasu arteritis, giant cell arteritis
  • Medium vessel: Polyarteritis nodosa
  • Small vessel: ANCA-associated vasculitis (GPA, MPA, EGPA), IgA vasculitis

• Clinical Assessment: Use validated tools like Birmingham Vasculitis Activity Score (BVAS) to assess disease activity and guide treatment decisions 1

Essential Diagnostic Tests

Biopsy

• Gold standard for diagnosis - strongly recommended to establish new diagnosis or evaluate suspected relapse 2
• Target selection based on affected organ:
  • Renal biopsy: Highest diagnostic yield (up to 91.5%) in GPA with renal involvement 2
  • ENT tissue: Up to 68.4% yield in GPA 2
  • Lung: Lower yield (12% for transbronchial biopsies in GPA) 2

Laboratory Testing

1. ANCA Testing:

   • Test for both PR3-ANCA and MPO-ANCA using high-quality antigen-specific assays 2
   • Immunofluorescence and ELISA methods recommended 1
   • Interpret in clinical context (positive ANCA alone is not diagnostic) 1

2. Basic Laboratory Studies:

   • Complete blood count with differential
   • Comprehensive metabolic panel
   • Inflammatory markers: ESR and CRP
   • Renal function: Serum creatinine, eGFR
   • Urinalysis with microscopic examination and protein quantification 1

3. Additional Serologic Testing:

   • Complement levels (C3, C4)
   • Hepatitis B and C serology
   • Cryoglobulins when appropriate
   • Immunoglobulin levels (especially if considering rituximab therapy) 1, 3

Imaging Studies

• Select based on suspected vessel size 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

Organ-Specific Evaluation

Renal Assessment

• Urinalysis with microscopic examination (hematuria, proteinuria)
• Protein/creatinine ratio
• Renal function tests
• Renal biopsy if indicated (gold standard for diagnosis of renal vasculitis) 1

Pulmonary Assessment

• Chest imaging (CT preferred over X-ray)
• Pulmonary function tests
• Bronchoscopy with bronchoalveolar lavage if pulmonary hemorrhage suspected
• Lung biopsy when appropriate 1

ENT Assessment

• Nasal endoscopy
• Sinus CT scan
• Biopsy of suspicious lesions 2

Important Considerations

1. Do not delay treatment in rapidly deteriorating patients with clinical presentation compatible with small-vessel vasculitis and positive MPO or PR3-ANCA while waiting for biopsy results 1

2. Refer to centers of expertise for complex cases or refractory disease, as AAV requires multidisciplinary management 2

3. Structured clinical assessment rather than ANCA testing alone should guide treatment decisions 2

4. Monitor for treatment complications including infections, which are common in treated patients 1

Common Pitfalls to Avoid

• Relying solely on ANCA testing without clinical correlation
• Delaying treatment in severe cases while waiting for biopsy results
• Failing to assess for specific organ involvement comprehensively
• Not considering mimics of vasculitis (infections, malignancy, drug reactions)
• Overlooking the need for periodic cardiovascular risk assessment in patients with vasculitis 1

By following this structured approach to diagnosis, clinicians can efficiently identify and classify vasculitis, enabling prompt initiation of appropriate treatment to improve outcomes and reduce morbidity and mortality.