The C-ANCA (PR3) Test measures antibodies against Proteinase 3 (PR3), an enzyme found in neutrophils (a type of white blood cell). The presence of C-ANCA/PR3 antibodies is strongly associated with granulomatosis with polyangiitis (GPA), formerly known as Wegener’s granulomatosis.

This autoimmune disorder causes inflammation and damage to small and medium-sized blood vessels, particularly affecting the lungs, kidneys, sinuses, and skin. The C-ANCA test helps with early detection, diagnosis, and monitoring of disease activity.

Why is the C-ANCA (PR3) Test Done?

This test is typically ordered to:

✔ Diagnose Granulomatosis with Polyangiitis (GPA) – A severe autoimmune disease affecting blood vessels.
✔ Differentiate between types of vasculitis – Helps distinguish GPA from other vasculitic disorders like Microscopic Polyangiitis (MPA).
✔ Monitor Disease Progression & Treatment Response – Tracks treatment effectiveness and disease relapses.
✔ Evaluate Symptoms of Autoimmune Vasculitis, such as:

• Chronic sinus infections.
• Persistent cough with or without blood (hemoptysis).
• Kidney problems (blood in urine, swelling).
• Skin rashes or ulcers.
• Joint pain and muscle aches.

Who Should Get This Test?

The C-ANCA (PR3) Test is recommended for:

✔ Individuals with suspected vasculitis, especially those with symptoms affecting the lungs, kidneys, and sinuses.
✔ Patients undergoing treatment for GPA, to monitor disease activity and response to therapy.
✔ Individuals with unexplained inflammatory symptoms that might indicate autoimmune vasculitis.

Test Procedure & Preparation

Preparation:

• No fasting is required.
• Inform your doctor about medications you are taking, as some may affect results.
• Avoid immunosuppressive drugs, if advised by your doctor, before the test.

Procedure:

1. A blood sample is drawn from a vein in the arm.
2. The sample is tested using ELISA (Enzyme-Linked Immunosorbent Assay) or Immunofluorescence.
3. Results are typically available within 1-3 days.

Understanding the Results

✔ Negative Result (Normal):

• No significant C-ANCA/PR3 antibodies detected, meaning low likelihood of GPA.

✔ Positive Result:

• Indicates elevated C-ANCA/PR3 antibodies, suggesting a high probability of GPA.
• Strongly correlates with active disease or relapse in GPA patients.

✔ Mildly Elevated Results:

• Could be due to other autoimmune diseases or inflammatory conditions.

⚠ A positive test alone does not confirm GPA. Additional tests (e.g., kidney function, lung imaging, biopsy) are needed for a definitive diagnosis.

Limitations of the Test

❌ Not a standalone diagnostic tool – Should be interpreted with clinical symptoms and other diagnostic tests.
❌ False positives/negatives – Some individuals with vasculitis may test negative, and some with other inflammatory conditions may test positive.
❌ Does not determine disease severity – Only indicates the presence of antibodies, not the extent of organ damage.

Why is the C-ANCA (PR3) Test Important?

✔ Helps in early detection of GPA, preventing severe complications.
✔ Assists in monitoring disease activity and treatment response.
✔ Aids in differentiating between different autoimmune vasculitides.

The C-ANCA (PR3) Test plays a critical role in diagnosing, managing, and monitoring granulomatosis with polyangiitis, ensuring timely and effective treatment for affected individuals.