What blood tests are included in a vasculitis screen?

From the Guidelines

A comprehensive vasculitis screen should include a complete blood count (CBC), erythrocyte sedimentation rate (ESR), C-reactive protein (CRP), comprehensive metabolic panel, urinalysis, antineutrophil cytoplasmic antibodies (ANCA) with both proteinase-3 (PR3) and myeloperoxidase (MPO) specificity, antinuclear antibody (ANA), rheumatoid factor (RF), complement levels (C3, C4), cryoglobulins, hepatitis B and C serologies, and anti-glomerular basement membrane (anti-GBM) antibodies, as these tests are crucial for diagnosing and evaluating inflammatory blood vessel disorders, as recommended by the kdigo 2024 clinical practice guideline for the management of antineutrophil cytoplasmic antibody (ANCA)-associated vasculitis 1.

Key Components of a Vasculitis Screen

• Complete blood count (CBC) to assess for anemia and leukocytosis
• Erythrocyte sedimentation rate (ESR) and C-reactive protein (CRP) as inflammatory markers
• Comprehensive metabolic panel to evaluate organ function
• Urinalysis to check for kidney involvement
• Antineutrophil cytoplasmic antibodies (ANCA) with both proteinase-3 (PR3) and myeloperoxidase (MPO) specificity
• Antinuclear antibody (ANA)
• Rheumatoid factor (RF)
• Complement levels (C3, C4)
• Cryoglobulins
• Hepatitis B and C serologies
• Anti-glomerular basement membrane (anti-GBM) antibodies

Importance of ANCA and Anti-GBM Antibodies

The diagnosis of ANCA-associated vasculitis relies on the combination of clinical findings and results of imaging studies and laboratory tests, including ANCA and anti-GBM antibodies 1. About 90% of patients with small-vessel vasculitis or necrotizing and crescentic glomerulonephritis (NCGN) have ANCA, directed primarily to the neutrophil granule proteins MPO or PR3 1. A positive test for anti-GBM antibodies suggests anti-GBM disease and a need for urgent plasma exchange, whereas a positive test for MPO- or PR3-ANCA supports a diagnosis of ANCA-associated vasculitis 1.

Clinical Implications

The pattern of positive results, combined with clinical features and possibly tissue biopsy, guides diagnosis and treatment decisions. The need to treat extrarenal vasculitis may influence treatment choices for kidney vasculitis, and a slowly progressive course has also been described when active vasculitic lesions may be hard to find on histology 1.

From the Research

Blood Tests Included in Vasculitis Screen

The following blood tests are typically included in a vasculitis screen:

• Erythrocyte sedimentation rate (ESR) 2, 3
• C-reactive protein (CRP) 2, 3
• Blood count 2, 4
• Serum creatinine 2, 4
• Urinalysis 2, 4
• Specific autoantibodies, such as:
  • Anti-neutrophil cytoplasmic antibodies (ANCAs) 2, 4
  • Anti-glomerular basement membrane (GBM) antibodies 2
  • Anti-C1q antibodies 2
• Complement levels, including C3 and C4 4
• Immunoglobulin levels 2
• Cryoglobulin levels 2
• Hepatitis B and C serology 2
• Procalcitonin 4
• Fibrinogen 4
• D-dimer 4
• Albumin 4
• Hemoglobin 4

Rationale for Each Test

These tests are used to help diagnose and monitor vasculitis, as well as to distinguish it from other inflammatory conditions. For example:

• ESR and CRP are nonspecific markers of inflammation, but can be helpful in monitoring disease activity 2, 3
• ANCA antibodies are specific for certain types of vasculitis, such as ANCA-associated small-vessel vasculitis 2, 4
• Complement levels can be helpful in diagnosing immune complex-associated small-vessel vasculitis 2
• Procalcitonin can be helpful in identifying infectious complications in patients with vasculitis 4