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

Appropriate Workup for Suspected Vasculitis

The appropriate workup for a patient suspected of having vasculitis should include complete blood count with differential, ANCA testing, renal function assessment, and targeted imaging based on suspected vessel size, with definitive diagnosis often requiring biopsy of affected tissue. 1

Initial Laboratory Evaluation

• Complete blood count with differential

  • Look for anemia, leukocytosis, and eosinophilia (>1500 cells/μl or >10% is characteristic of active EGPA)
  • Leukopenia may be present in some forms of vasculitis

• Inflammatory markers

  • Erythrocyte sedimentation rate (ESR)
  • C-reactive protein (CRP)

• Renal function assessment

  • Serum creatinine
  • Blood urea nitrogen (BUN)
  • Estimated glomerular filtration rate (eGFR)
  • Urinalysis with microscopic examination to detect hematuria, proteinuria, or casts

• 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
  • ANCA testing provides 99% specificity with 73% sensitivity for GPA 1

• Additional serological testing

  • Complement levels (C3, C4)
  • Hepatitis B and C serology (particularly important with liver involvement)
  • Cryoglobulins
  • Anti-phospholipase-A2-receptor antibodies (in suspected cryoglobulinemic vasculitis)

Imaging Studies Based on Suspected Vessel Size

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

Tissue Biopsy

• Biopsy of affected tissue is the gold standard for definitive diagnosis

• For cutaneous vasculitis, biopsy should:

  • Extend to the subcutis
  • Be taken from the most tender, reddish, or purpuric lesional skin
  • Include serial sections to identify the main vasculitic lesion
  • Include direct immunofluorescence to distinguish IgA-associated vasculitis (Henoch-Schönlein purpura) from IgG/IgM-associated vasculitis 1

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

Diagnostic Approach Algorithm

1. Assess clinical presentation and suspected vessel size involvement

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

2. Order initial laboratory tests

   • CBC with differential, renal function, inflammatory markers, ANCA, complement levels

3. Order appropriate imaging based on suspected vessel size and organ involvement

4. Perform tissue biopsy of affected organ when possible

   • If ANCA positive with compatible clinical presentation, consider starting treatment before biopsy results

5. Exclude secondary causes of vasculitis

   • Infections
   • Medications
   • Malignancies
   • Connective tissue diseases

Special Considerations

• For suspected pulmonary vasculitis:

  • Chest CT is more useful than chest radiography for assessing thoracic involvement 2
  • Look for vessel wall thickening, nodular or cavitary lesions, ground-glass opacities, and consolidations

• For cutaneous vasculitis:

  • Look for palpable purpura, infiltrated erythema, nodular erythema, livedo racemosa, deep ulcers, or digital gangrene
  • Coexistence of pan-dermal small-vessel vasculitis and subcutaneous muscular-vessel vasculitis usually indicates CTD, ANCA-associated vasculitis, Behçet disease, or malignancy-associated vasculitis 3

• For leukocytoclastic vasculitis:

  • Extensive workup is necessary to determine whether the process is skin-limited or expression of a systemic vasculitis 4

Monitoring and Follow-up

• Regular assessment of disease activity using validated tools like the Birmingham Vasculitis Activity Score
• Monitoring of ANCA levels in ANCA-associated vasculitis
• Regular urinalysis and renal function tests to detect kidney involvement
• Vigilance for treatment complications, especially infections 1

Referral Recommendation

Patients with suspected vasculitis should be referred to centers with experience in vasculitis management for optimal care, particularly those with suspected or confirmed ANCA-associated vasculitis 1