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Blood Test Tracker

PR3-ANCA (Anti-Proteinase 3 Antibody)

A blood test for antibodies against proteinase 3, a protein in white blood cells. A positive result is most linked to granulomatosis with polyangiitis, a type of vasculitis.

AI-verified against cited sources. Awaiting expert reviewAlso called PR3-ANCA, PR3 Ab, Anti-PR3LOINC 46267-1

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What it is

White blood cells called neutrophils contain a protein named proteinase 3 (PR3). Sometimes the immune system makes antibodies against it. These are called PR3-ANCA, short for anti-neutrophil cytoplasmic antibodies. This test measures them in a blood sample. Each lab uses its own test kit with its own units and cutoff, so read your number next to the range on your own report.

Why it matters

PR3 antibodies are the typical finding in granulomatosis with polyangiitis (GPA), a rare condition in which small blood vessels become inflamed. GPA often involves the nose and sinuses, the lungs and the kidneys. In the 2022 ACR/EULAR classification criteria for GPA, which are used mainly in research, a PR3 antibody or c-ANCA result carries the biggest positive weight (+5 points). A positive result is one clue among many, and your clinician reads it with your symptoms, urine and kidney tests, imaging and sometimes a tissue sample. A negative result does not rule vasculitis out.

If it’s high

A result above your lab's cutoff means antibodies against PR3 were found. With the right symptoms, this fits with GPA. PR3 antibodies can also show up for other reasons, and a low-level result is less specific. A positive result by itself is not a diagnosis.

Common causes

  • A low-level positive that other tests do not back up, which is why labs sometimes add a second test such as the ANCA microscope test
  • Infection of the heart valves (infective endocarditis), where most ANCA-positive cases show a c-ANCA or PR3 pattern
  • Cocaine mixed with levamisole, and some medicines
  • Bowel conditions, which can cause ANCA patterns that are not always aimed at PR3 or MPO
  • Granulomatosis with polyangiitis, the condition most linked to PR3 antibodies
  • Other ANCA-associated vasculitis, less often

What can help

  • Ask whether the result should be checked with a second test, such as the ANCA microscope test or an MPO antibody test
  • Ask whether kidney function, urine tests or a chest scan make sense for your symptoms
  • Ask whether an infection or any of your medicines could be linked to this result
  • Keep track of symptoms such as a bloody or crusted nose, sinus problems that will not clear, hearing loss, a cough that will not go away and blood in the urine, and share them with your clinician

Usual ranges

What labs print as the reference range, by who was tested. Ranges differ a little between labs, so the range on your own report is the one your result is judged against.

For adults: 0–19 AU/mL. Source: ARUP Laboratories.

What can affect your result

  • Test method: kits differ in units and cutoffs, so only compare results from the same lab and kit
  • Treatment and disease activity: levels can fall with treatment
  • Infections and other conditions that can trigger ANCA
  • Sample quality: heavily hemolyzed or very fatty (lipemic) samples can be rejected
  • Kits differ in units and cutoffs (AU/mL at ARUP, antibody index at Quest, U at Mayo, U/mL at Labcorp), so results from different labs cannot be compared with each other.
  • Samples with gross hemolysis can be rejected by the lab (ARUP, Quest). ARUP also rejects lipemic samples and does not accept plasma for this test.
  • Cocaine mixed with levamisole and some other medicines can cause positive ANCA results.
  • Infection of the heart valves (infective endocarditis) can cause positive ANCA results, mostly with a c-ANCA or PR3 pattern.

Levels can fall with treatment, but Mayo Clinic Laboratories advises against relying on the number alone to judge treatment response or flare risk.

When to talk to a clinician

If your lab or clinician has not already contacted you about a positive result, call the clinician who ordered the test soon. Talk with a clinician promptly about a bloody or crusted nose, sinus problems that will not clear, hearing loss, a cough that will not go away, or blood or foam in your urine. Call 911 or your local emergency number if you cough up blood or have severe trouble breathing.

Questions you could ask

  • Which method and units does my lab use, and how should I compare future results?
  • Should this result be confirmed with a second test?
  • Do my symptoms mean I should have kidney, urine or lung tests?
  • Could an infection or any of my medicines explain this result?
  • Which specialist should I see next?

Questions people ask

What is the difference between c-ANCA and PR3-ANCA?

c-ANCA is the glow pattern seen under a microscope. PR3-ANCA is a blood test that finds the specific protein (PR3) the antibody attaches to. Most c-ANCA patterns come from PR3 antibodies, but not all, so labs often run both.

Does a positive PR3-ANCA mean I have GPA?

Not by itself. Mayo Clinic Laboratories notes that a positive result is not diagnostic and has to be read with your symptoms and other tests. Infections and some other conditions can also cause it.

Can the test be negative if I have ANCA-associated vasculitis?

Yes. Mayo Clinic Laboratories states that negative results do not exclude it. Your clinician looks at your symptoms and other tests too.

Show the science and sources

For clinicians and researchers

PR3-ANCA are IgG autoantibodies to proteinase 3, a serine protease in neutrophil granules. On ethanol-fixed neutrophils they give a granular cytoplasmic (c-ANCA) pattern, and ARUP reports that about 85% of people with a c-ANCA pattern by IFA have PR3 specificity. Mayo notes that patients with GPA frequently have PR3 antibodies, while those with MPA or EGPA are more likely to have MPO antibodies. The 2017 international consensus (Bossuyt et al.) proposes that high-quality antigen-specific immunoassays can be the primary screen for suspected GPA or MPA without a categorical need for IFA, and Mayo adds that the ANCA microscope test can be used when suspicion is high but PR3 and MPO immunoassays are negative, or to improve specificity when a result is low-positive. In the 2022 ACR/EULAR GPA criteria, c-ANCA or anti-PR3 positivity scores +5 and p-ANCA or anti-MPO positivity scores -1; in the MPA criteria, c-ANCA or anti-PR3 positivity scores -1. Reference intervals are kit-specific: ARUP (multiplex bead) 19 AU/mL or less negative, 20 to 25 equivocal, 26 or more positive; Quest (immunoassay) below 1.0 AI; Mayo below 0.4 U negative, 0.4 to 0.9 equivocal, 1.0 or more positive; Labcorp (EliA) below 2.0 U/mL negative, 2.0 to 3.0 equivocal, above 3.0 positive. Mayo cautions that a positive result is not diagnostic, a negative result does not exclude AAV, and serial PR3-ANCA levels should not be relied on exclusively to judge response or flare risk. In a systematic review of ANCA-positive infective endocarditis, 79% of cases had a c-ANCA pattern or PR3 antibodies and 69% became ANCA-negative after treatment, with no vasculitis diagnosed.

LOINC 46267-1 (primary), 6968-2, 74106-6, 48408-9, 63310-7. Specimen: serum.

Sources

  1. Serine Proteinase 3 (PR3) Antibody (test 0050527), ARUP Laboratories
  2. Proteinase-3 Antibody (test 34151), Quest Diagnostics
  3. Proteinase 3 Antibodies, IgG, Serum (test PR3), Mayo Clinic Laboratories
  4. Antiproteinase 3 (PR3) Antibodies (test 163067), Labcorp
  5. ANCA Screen with Reflex to ANCA Titer (test 70171), Quest Diagnostics
  6. MPO/PR3 (ANCA) Antibodies (test 0050707), ARUP Laboratories
  7. Position paper: Revised 2017 international consensus on testing of ANCAs in granulomatosis with polyangiitis and microscopic polyangiitis, Nature Reviews Rheumatology (2017)
  8. Detection of antineutrophil cytoplasmic antibodies (ANCAs): a multicentre European Vasculitis Study Group (EUVAS) evaluation of the value of indirect immunofluorescence (IIF) versus antigen-specific immunoassays, Annals of the Rheumatic Diseases (2017)
  9. 2022 American College of Rheumatology/European Alliance of Associations for Rheumatology classification criteria for granulomatosis with polyangiitis, Annals of the Rheumatic Diseases (ACR/EULAR) (2022)
  10. 2022 American College of Rheumatology/European Alliance of Associations for Rheumatology classification criteria for microscopic polyangiitis, Annals of the Rheumatic Diseases (ACR/EULAR) (2022)
  11. Antineutrophil Cytoplasmic Antibodies (ANCA) Test, MedlinePlus (U.S. National Library of Medicine)
  12. Trojan horses: drug culprits associated with antineutrophil cytoplasmic autoantibody (ANCA) vasculitis, Current Opinion in Rheumatology (2014)
  13. Antineutrophil cytoplasmic antibodies in infective endocarditis: a case report and systematic review of the literature, Clinical Rheumatology (2022)

AI-verified against cited sources. Awaiting expert review. Last reviewed 2026-10-03. How we build and check these pages.

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