What laboratory tests are used to diagnose and manage vasculitis?

Laboratory Tests for Diagnosing and Managing Vasculitis

A comprehensive ANCA panel with immunofluorescence and ELISA for PR3/MPO antibodies is the cornerstone laboratory test for diagnosing vasculitis, particularly ANCA-associated vasculitis. 1

Essential Laboratory Tests for Initial Diagnosis

Core Tests

• Complete blood count with differential

  • Look for anemia, leukocytosis, eosinophilia (>1500 cells/μl or >10% particularly important for EGPA) 1
  • Thrombocytosis may indicate active inflammation

• Inflammatory markers

  • Erythrocyte sedimentation rate (ESR)
  • C-reactive protein (CRP)
  • Note: While elevated in active vasculitis, these are nonspecific and cannot differentiate between disease activity and infection 2

• Renal function assessment

  • Serum creatinine
  • Estimated GFR (using MDRD or Cockroft-Gault equations) 1
  • Urinalysis with microscopic examination (looking for hematuria, red cell casts)
  • Quantification of proteinuria (>3g/day indicates significant glomerular damage) 1

• Autoantibody testing

  • ANCA panel with immunofluorescence and ELISA for PR3/MPO specificity 1, 2
  • Anti-glomerular basement membrane (GBM) antibodies
  • Antinuclear antibodies (ANA)
  • Anti-dsDNA antibodies
  • Anti-CCP antibodies (for differential diagnosis) 1

Additional Tests Based on Clinical Presentation

• Complement levels (C3, C4) - particularly for immune complex vasculitis 2
• Immunoglobulin levels - especially before rituximab therapy 3
• Hepatitis B and C serology - essential for all patients with suspected vasculitis 1, 2
• Cryoglobulins - for suspected cryoglobulinemic vasculitis 2
• Anti-phospholipase-A2-receptor antibodies - if membranous nephropathy is suspected 4

Laboratory Tests for Disease Monitoring

• Serial inflammatory markers (ESR, CRP) - to assess disease activity 1
• Complete blood count - to monitor for treatment-related cytopenias
• Renal function tests - especially in vasculitis with kidney involvement
• Serial urinalysis - to detect early renal involvement or relapse
• ANCA levels - particularly useful for monitoring disease activity in ANCA-associated vasculitis 1, 2
• Immunoglobulin levels - prior to each course of rituximab 3

Important Considerations

• Timing is critical: Do not delay treatment while awaiting biopsy results in rapidly progressive disease 3, 1
• Clinical correlation is essential: Laboratory tests must be interpreted in the clinical context, as they are not specific in isolation 1
• Biopsy remains the gold standard: Laboratory tests support but do not replace histopathological confirmation when feasible 3
• Cardiovascular risk assessment: Regular monitoring of traditional cardiovascular risk factors is important due to increased risk in vasculitis patients 3

Disease-Specific Considerations

ANCA-Associated Vasculitis (GPA, MPA, EGPA)

• ANCA testing with both immunofluorescence and antigen-specific immunoassays
• PR3-ANCA is more common in GPA, while MPO-ANCA is more common in MPA 2
• Complete blood count (eosinophilia >10% is characteristic of EGPA)

Large Vessel Vasculitis (GCA, Takayasu Arteritis)

• ESR and CRP are particularly important
• Temporal artery biopsy should be performed when GCA is suspected, but should not delay treatment 3

Medium Vessel Vasculitis (PAN)

• Hepatitis B and C serology
• Renal function tests and urinalysis
• Angiography may be necessary for diagnosis 4

Small Vessel Vasculitis

• ANCA, anti-GBM antibodies
• Urinalysis and renal function tests
• Complement levels and cryoglobulins 2

Remember that vasculitis is a complex group of disorders requiring multidisciplinary management at centers with specific expertise in vasculitis 3, 1.