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

Appropriate Workup for Suspected Vasculitis

The appropriate workup for suspected vasculitis should include complete blood count with differential, ANCA testing, comprehensive renal function assessment, inflammatory markers, and targeted imaging based on suspected vessel size, followed by tissue biopsy from affected organs when clinically indicated. 1

Initial Laboratory Evaluation

• Complete blood count with differential

  • Look for anemia, leukocytosis, and eosinophilia (>1500 cells/μl or >10% suggests EGPA) 1
  • Platelet count to assess for thrombocytopenia or thrombocytosis

• Inflammatory markers

  • Erythrocyte sedimentation rate (ESR)
  • C-reactive protein (CRP)
  • Monitor these serially to assess disease activity and treatment response 1

• ANCA testing

  • Indirect immunofluorescence for c-ANCA and p-ANCA patterns
  • ELISA for specific antibodies (PR3-ANCA and MPO-ANCA)
  • PR3-ANCA (c-ANCA) is highly specific for GPA (Wegener's)
  • MPO-ANCA (p-ANCA) is associated with MPA and EGPA 1
  • ANCA testing provides 99% specificity with 73% sensitivity for GPA 1

• Renal function assessment

  • Serum creatinine
  • Blood urea nitrogen (BUN)
  • Estimated glomerular filtration rate (eGFR)
  • Urinalysis with microscopic examination (look for hematuria, proteinuria, casts) 1

• Complement levels

  • C3 and C4 levels to assess for hypocomplementemic vasculitis 2, 3

• Additional serological testing

  • Hepatitis B and C serology (particularly important with liver involvement) 1, 2, 3
  • Cryoglobulins (for suspected cryoglobulinemic vasculitis) 1
  • Anti-phospholipase-A2-receptor antibodies (for membranous nephropathy) 1
  • Antinuclear antibodies (ANA) to assess for connective tissue disease-associated vasculitis 3

Imaging Studies

Imaging should be targeted based on suspected vessel size and clinical presentation:

• Large vessel vasculitis (Takayasu arteritis, Giant cell arteritis)

  • CT/CTA, MRI/MRA, or FDG-PET/CT 1

• Medium vessel vasculitis (Polyarteritis nodosa)

  • CTA of affected regions (renal, mesenteric, coronary) 1

• Small vessel vasculitis (ANCA-associated, immune complex)

  • MRI/MRA or FDG-PET/CT as clinically indicated 1
  • Chest imaging for pulmonary involvement

Tissue Biopsy

• Biopsy is the gold standard for definitive diagnosis 2, 3

  • Should be performed whenever there is access to clinically affected tissue 2
  • For cutaneous vasculitis: biopsy from the most tender, reddish or purpuric lesional skin, extending to the subcutis 4
  • Consider serial sections to identify the main vasculitic lesion 4

• Direct immunofluorescence

  • Concomitant biopsy for direct immunofluorescence helps distinguish:
    • IgA-associated vasculitis (Henoch-Schönlein purpura)
    • IgG/IgM-associated vasculitis 4, 3

Special Considerations

• If ANCA positive with compatible clinical presentation, treatment should not be delayed while waiting for biopsy results, especially in rapidly deteriorating patients 1

• If ANCA negative with compatible clinical presentation, biopsy is essential for definitive diagnosis 1

• Patients with suspected vasculitis should be referred to centers with experience in vasculitis management for optimal care 1

• Monitor disease activity using validated tools such as the Birmingham Vasculitis Activity Score 1

Common Pitfalls to Avoid

1. Delaying treatment in rapidly progressive disease while waiting for biopsy results
2. Failing to exclude vasculitis mimics (pseudovasculitis) such as thrombotic disorders, antiphospholipid syndrome, or embolic phenomena 4
3. Inadequate biopsy sampling - ensure adequate depth and size of tissue sample
4. Not considering underlying causes - always evaluate for infections, medications, malignancies, and connective tissue diseases 3
5. Missing systemic involvement - cutaneous manifestations may be the presenting feature of systemic vasculitis requiring thorough evaluation of other organ systems 4, 5

By following this systematic approach to the workup of suspected vasculitis, clinicians can establish an accurate diagnosis, determine disease extent, and initiate appropriate treatment to improve outcomes and reduce morbidity and mortality.