ANCA/MPO/PR3 Antibodies

You don’t need to do anything special to prepare for this test. You can eat and drink normally beforehand. 

The test uses a blood sample taken from a vein in your arm. 

Because this is a specialised test, your sample will be sent to a clinical immunology laboratory. Results usually take about 3 working days. 

What the test measures 

This test looks for abnormal antibodies in your blood called ANCA (antineutrophil cytoplasmic antibodies). These are autoantibodies – antibodies that mistakenly attack your own body instead of fighting infection. 

ANCA targets two specific proteins inside white blood cells called neutrophils. These proteins are myeloperoxidase (MPO) and proteinase 3 (PR3). 

When your immune system produces antibodies against MPO or PR3, it causes inflammation that damages small blood vessels throughout your body. This damage is called vasculitis. 

The test checks for antibodies against MPO and PR3. Some laboratories also perform an additional test using fluorescent microscopy to see the pattern of antibody staining. 

What your results mean 

Your doctor will interpret results carefully, considering your symptoms and other test results. Positive ANCA tests help diagnose vasculitis, but a tissue biopsy is usually needed to confirm the diagnosis. 

PR3 antibodies (proteinase 3) 

If you have high levels of PR3 antibodies: 

• You may have granulomatosis with polyangiitis (GPA), formerly called Wegener’s granulomatosis 
• About 90% of people with active GPA have PR3 antibodies 
• When disease is less active, 60–70% still have detectable PR3 antibodies 

GPA typically affects the nose, sinuses, lungs, and kidneys. It causes inflammation that can damage these organs if not treated. 

MPO antibodies (myeloperoxidase) 

If you have MPO antibodies, you may have: 

• Microscopic polyangiitis: about 60% of patients have MPO antibodies 
• Eosinophilic granulomatosis with polyangiitis (EGPA): formerly Churg-Strauss syndrome – 50–80% have MPO antibodies 
• Kidney inflammation: necrotising glomerulonephritis 

MPO antibodies can also occasionally appear in other autoimmune conditions like lupus, rheumatoid arthritis, and Sjögren syndrome. 

About 30% of people with microscopic polyangiitis have PR3 antibodies instead of MPO antibodies. 

Negative results 

If both MPO and PR3 antibodies are negative, it’s much less likely that your symptoms are caused by ANCA-associated vasculitis. 

However, a negative result doesn’t completely rule out vasculitis. Some people with vasculitis don’t have detectable ANCA, especially in less active disease. 

Fluorescence patterns 

Some laboratories perform an additional microscopy test to confirm positive results. This shows different patterns: 

• c‑ANCA (cytoplasmic pattern): about 85% of samples show PR3 antibodies 
• p‑ANCA (perinuclear pattern): about 90% of samples show MPO antibodies 

If your ANCA test is positive 

Your doctor will usually: 

• Arrange imaging scans (chest X‑ray, CT scan) to look for organ damage 
• Request a tissue biopsy to confirm vasculitis (usually kidney or lung) 
• Order additional blood tests to check organ function 
• Refer you to a specialist (rheumatologist or renal physician ) 

If vasculitis is confirmed 

Treatment usually involves: 

• Immunosuppressive drugs to calm your immune system (cyclophosphamide, rituximab, or methotrexate) 
• Steroids (prednisolone) to reduce inflammation 
• Regular monitoring with blood tests and scans 

With treatment, many people with vasculitis can achieve remission. However, the condition can relapse, so ongoing monitoring is important. 

Monitoring during treatment 

You’ll have regular tests to: 

• Check if ANCA levels are falling (shows treatment is working) 
• Monitor kidney and liver function 
• Watch for disease relapse (rising ANCA levels) 
• Check for treatment side effects 

What can affect your results 

Several conditions can cause positive ANCA tests without vasculitis being present: 

• Other autoimmune diseases: lupus, rheumatoid arthritis, inflammatory bowel disease 
• Certain medications: some drugs can trigger ANCA production 
• Cocaine use: levamisole can trigger ANCA production 
• Infections: heart infection (endocarditis) or severe respiratory infections 

A positive ANCA in these conditions doesn’t mean you have vasculitis. Your doctor will consider all your symptoms and test results together. 

ANCA levels can fluctuate over time. Once you develop these autoantibodies, they typically persist even during remission, though levels may vary. 

ANCA testing is usually done alongside other tests: 

Blood tests: 

• ESR (erythrocyte sedimentation rate) – measures inflammation 
• CRP (C‑reactive protein) – another inflammation marker 
• Full blood count – checks white and red blood cells 
• Creatinine and urea – checks kidney function 
• Complement levels – measures immune system proteins 

Urine tests: 

• Urinalysis – checks for blood and protein in urine (signs of kidney damage) 

Other autoantibody tests: 

• ANA (antinuclear antibodies) – for lupus and other conditions 
• Anti-GBM antibodies – for Goodpasture’s syndrome 

Imaging and biopsies: 

• Chest X‑ray or CT scan 
• Kidney biopsy 
• Lung biopsy or nasal tissue biopsy 

Vasculitis is a group of conditions where blood vessels become inflamed. ANCA-associated vasculitis specifically affects small blood vessels throughout the body. 

The inflammation damages vessel walls, narrowing or blocking them. This reduces blood supply to organs and tissues, causing damage. Weakened vessel walls can also develop bulges called aneurysms. 

The main types of ANCA-associated vasculitis are granulomatosis with polyangiitis (GPA), microscopic polyangiitis (MPA), and eosinophilic granulomatosis with polyangiitis (EGPA). Each affects slightly different organs but all involve small vessel inflammation. 

Learn more about vasculitis on Vasculitis UK and the NHS website