Anti-Neutrophil Cytoplasmic Antibody (ANCA) – PR3 Antibodies Test

The Anti-Proteinase 3 (PR3) Antibody Test detects autoantibodies against proteinase 3 (PR3), an enzyme found in neutrophils. It is primarily used to diagnose and monitor ANCA-associated vasculitis (AAV), particularly Granulomatosis with Polyangiitis (GPA, formerly Wegener’s granulomatosis).

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Why is the PR3 Antibody Test Done?

✅ To Diagnose ANCA-Associated Vasculitis (AAV)

• Granulomatosis with Polyangiitis (GPA) – A systemic small-vessel vasculitis affecting the respiratory tract and kidneys

✅ To Differentiate Between Types of Vasculitis

• PR3-ANCA (c-ANCA) is strongly associated with GPA
• MPO-ANCA (p-ANCA) is linked to Microscopic Polyangiitis (MPA) & Eosinophilic Granulomatosis with Polyangiitis (EGPA)

✅ To Monitor Disease Activity & Treatment Response

• PR3 antibody levels may correlate with disease severity
• Helps track response to immunosuppressive therapy

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Test Procedure

🩸 Blood Sample Collection:

• A blood sample is drawn from a vein
• No fasting required
• Results available in 3–7 days

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Normal Range & Interpretation

🔹 A positive PR3-ANCA test does NOT confirm disease on its own; clinical correlation is needed.
🔹 Some patients with active vasculitis may test negative for PR3-ANCA.

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What Do Abnormal PR3 Antibody Levels Mean?

🔴 High PR3-ANCA Levels Suggest:

• Granulomatosis with Polyangiitis (GPA) – Most common association
• Pauci-immune Glomerulonephritis (Severe kidney condition)
• Systemic Vasculitis with Lung & Kidney Involvement

🟢 Negative PR3-ANCA:

• GPA is unlikely
• If symptoms persist, MPO-ANCA (p-ANCA), kidney biopsy, or further tests may be needed

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Next Steps If PR3-ANCA Is Positive?

🔬 Additional Tests for Confirmation:

• MPO-ANCA (p-ANCA) Test – Helps differentiate Microscopic Polyangiitis (MPA)
• Kidney Function Tests (Creatinine, eGFR, Urinalysis, Proteinuria, RBC casts)
• CRP & ESR (Inflammatory Markers) – Elevated in active vasculitis
• Chest X-ray / CT Scan – To check for lung involvement in vasculitis
• Kidney or Lung Biopsy – To confirm diagnosis in unclear cases

✅ Treatment for PR3-ANCA-Associated Conditions:

• Corticosteroids (Prednisone) & Immunosuppressants (Rituximab, Cyclophosphamide)
• Plasma Exchange (PLEX) in severe cases (e.g., rapidly progressive glomerulonephritis)
• Regular Monitoring of PR3-ANCA Levels to track disease activity

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Key Takeaways

🔹 PR3-ANCA is a key marker for Granulomatosis with Polyangiitis (GPA).
🔹 A positive test should be correlated with clinical symptoms and other lab findings.
🔹 Early diagnosis & treatment can prevent severe organ damage.
🔹 Long-term monitoring is needed for disease recurrence.