What bloodwork is necessary for the diagnosis of vasculitis?

Bloodwork for Vasculitis Diagnosis

The diagnosis of vasculitis requires a comprehensive laboratory workup including complete blood count, inflammatory markers (ESR, CRP), renal function tests, urinalysis, and ANCA testing with immunofluorescence and ELISA for PR3/MPO antibodies, along with specific tests based on suspected vessel size and clinical presentation. 1

Core Laboratory Tests for All Suspected Vasculitis Cases

• Inflammatory markers:

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

• Complete blood count with differential:

  • Neutrophil-to-lymphocyte ratio (NLR) may be elevated 2
  • Red blood cell distribution width (RDW) assessment

• Renal function assessment:

  • Serum creatinine
  • Estimated glomerular filtration rate (eGFR)
  • Urinalysis with microscopic examination

• Autoantibody testing:

  • ANCA testing with both:
    • Immunofluorescence (for cytoplasmic or perinuclear patterns)
    • ELISA for PR3-ANCA and MPO-ANCA (high-quality antigen-specific assays) 1, 3

• Complement studies:

  • C3 and C4 levels

• Immunoglobulin levels

• Viral serology:

  • Hepatitis B and C testing (particularly important with liver involvement) 1, 3

Additional Tests Based on Suspected Vasculitis Type

Small Vessel Vasculitis

• Anti-glomerular basement membrane (GBM) antibodies
• Anti-C1q antibodies (for immune complex-associated vasculitis)
• Cryoglobulins
• Anti-phospholipase-A2-receptor antibodies (if membranous nephropathy suspected) 1, 3

Medium Vessel Vasculitis

• Hepatitis B and C serology (especially for polyarteritis nodosa)
• Specific organ function tests based on clinical presentation

Large Vessel Vasculitis

• Inflammatory markers are particularly important (ESR, CRP)
• No specific serological markers; diagnosis often relies on imaging 4, 1

Important Considerations

• Biopsy remains the gold standard for definitive diagnosis when feasible, with laboratory tests providing supportive evidence 1

• ANCA testing has high specificity for ANCA-associated vasculitis (particularly Wegener's granulomatosis/GPA and microscopic polyangiitis) but should be interpreted in clinical context 3

• The persistence of ANCA positivity is strongly associated with relapses, though an increase in ANCA titers has limited predictive value for subsequent relapse 5

• Routine laboratory tests may be nonspecific but provide useful information when combined with clinical presentation 3, 6

• Serial measurements of inflammatory markers and autoantibodies are valuable for monitoring disease activity and treatment response 1, 5

Pitfalls to Avoid

• Do not rely solely on ANCA testing for diagnosis or treatment decisions; structured clinical assessment is essential 1

• Elevated inflammatory markers (ESR, CRP) are nonspecific and cannot distinguish between vasculitis activity and concurrent infection 3

• Do not exclude vasculitis based on negative laboratory findings if clinical suspicion is high; some patients may have normal laboratory values despite active disease

• Remember that different ANCA subtypes (PR3-ANCA vs. MPO-ANCA) are associated with different clinical features and should guide further workup 3

• Laboratory testing should always be interpreted alongside imaging studies and, when possible, histopathological confirmation 4, 1