What is the initial workup for suspected vasculitis?

Initial Workup for Suspected Vasculitis

Begin with essential laboratory tests (CBC, CMP, ESR, CRP, urinalysis), ANCA testing for small vessel disease, and obtain tissue biopsy from affected organs whenever accessible, as biopsy remains the gold standard for definitive diagnosis. 1, 2

Laboratory Evaluation

Essential Initial Tests

• Complete blood count with differential to assess for anemia, thrombocytopenia, or leukocytosis 1, 2
• Comprehensive metabolic panel to evaluate renal function and electrolyte abnormalities 1, 2
• Inflammatory markers: ESR and CRP are critical for diagnosis and monitoring, though they lack specificity 3, 1
• Urinalysis is mandatory to detect hematuria, proteinuria, and red cell casts suggesting renal involvement 1, 2

Autoimmune Serologies

• ANCA testing using both indirect immunofluorescence AND ELISA when small vessel vasculitis is suspected 3, 1
• The 2017 international consensus recommends high-quality antigen-specific immunoassays (MPO-ANCA and PR3-ANCA) as the preferred screening method 1
• Important caveat: Approximately 10% of patients with clinical features of ANCA-associated vasculitis may be ANCA-negative, requiring tissue biopsy for definitive diagnosis 1, 2
• Anti-nuclear antibodies to evaluate for connective tissue diseases 2

Additional Laboratory Tests Based on Clinical Suspicion

• Hepatitis B and C serologies, particularly if liver involvement or cryoglobulinemia is suspected 3, 4
• Serum cryoglobulins when HCV-related vasculitis is considered 3
• 24-hour urine collection for protein and creatinine clearance if renal involvement is suspected 2

Imaging Studies

Selection Based on Vessel Size

For Large Vessel Vasculitis (Giant Cell Arteritis, Takayasu Arteritis):

• Thorough imaging assessment of the arterial tree using MRI/MRA or PET is recommended when large vessel vasculitis is suspected 3, 1, 5
• Temporal artery ultrasound shows 88% sensitivity and 97% specificity for Giant Cell Arteritis 1, 5
• FDG-PET/CT demonstrates inflammatory cell accumulation in vessel walls with high sensitivity and specificity 1, 5
• CT angiography provides excellent spatial resolution for evaluating both vessel walls and lumen 3, 5

For CNS Vasculitis:

• MRI brain is the preferred initial imaging modality, showing abnormal findings in >90% of cases 3, 5
• Transcranial color-Doppler ultrasonography may be useful 3
• MRI is more sensitive than CT except for large ischemic infarctions and hemorrhage 3

For Pulmonary Involvement:

• Chest X-ray or CT to evaluate for pulmonary infiltrates, granulomas, cavitary lesions, or hemorrhage 2

Tissue Biopsy - The Gold Standard

Biopsy of affected tissue is strongly recommended and remains the definitive diagnostic test for vasculitis. 3, 1, 6

Biopsy Strategy

• Temporal artery biopsy should be performed whenever Giant Cell Arteritis is suspected, but this should not delay treatment initiation 3
• Kidney biopsy provides both diagnostic and prognostic information in suspected renal vasculitis, with diagnostic yield as high as 91.5% in ANCA-associated vasculitis 3, 1, 2
• Skin biopsy extending to the subcutis from the most tender, reddish, or purpuric lesional skin is key for cutaneous vasculitis; serial sections are often required 6
• Concomitant biopsy for direct immunofluorescence helps distinguish IgA-associated vasculitis (Henoch-Schönlein purpura) from IgG-/IgM-associated vasculitis 6
• The diagnostic yield of biopsies demonstrating either granuloma or vasculitis is over 70%, varying by organ sampled 1

Important Biopsy Considerations

• Otorhinolaryngological biopsies in GPA may show inflammatory changes in up to 68.4% of cases 3
• Lung biopsies have variable sensitivity: only 12% for transbronchial biopsies in GPA but 66.7% for EGPA 3
• Brain biopsy is the most specific test for diffuse or multifocal CNS vasculitis but is limited by its invasive nature 5

Critical Management Principles

• Patients with suspected vasculitis should be managed at centers with expertise in vasculitis to ensure optimal outcomes 3, 1, 2
• Use structured clinical assessment tools such as the Birmingham Vasculitis Activity Score (BVAS) at each visit 1
• Do not delay treatment while awaiting biopsy results if Giant Cell Arteritis is strongly suspected 3

Special Clinical Scenarios

Pulmonary-Renal Syndrome:

• Acute kidney injury with alveolar hemorrhage should immediately raise concern for vasculitis 1
• Positive anti-GBM antibodies suggest anti-GBM disease, while positive MPO or PR3-ANCA supports ANCA-associated vasculitis 1
• Pulmonary hemorrhage affects 10% of ANCA-associated vasculitis patients and increases mortality risk 1