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Blood Test Tracker

MPO-ANCA (Anti-Myeloperoxidase Antibody)

A blood test for antibodies against myeloperoxidase, a protein in white blood cells. A positive result is linked to some types of blood vessel inflammation (vasculitis).

AI-verified against cited sources. Awaiting expert reviewAlso called MPO-ANCA, MPO Ab, Anti-MPOLOINC 46266-3

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What it is

White blood cells called neutrophils contain a protein named myeloperoxidase (MPO). Sometimes the immune system makes antibodies against it. These are called MPO-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. This is not the same as the MPO test on some heart-risk panels, which measures the protein itself.

Why it matters

MPO antibodies are a key finding in ANCA-associated vasculitis, a group of rare conditions in which small blood vessels become inflamed. They are most linked to microscopic polyangiitis and eosinophilic granulomatosis with polyangiitis, and less often to granulomatosis with polyangiitis. The kidneys, lungs, nerves and skin can be affected. A positive result is one clue among many. Your clinician reads it together with your symptoms, urine and kidney tests, imaging and sometimes a tissue sample. A negative result does not rule these conditions out.

If it’s high

A result above your lab's cutoff means antibodies against MPO were found. With the right symptoms, this fits with ANCA-associated vasculitis, most often microscopic polyangiitis. MPO 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
  • Reactions to some medicines, including hydralazine, minocycline and propylthiouracil, or to cocaine mixed with levamisole
  • Infection of the heart valves (infective endocarditis), which can look like vasculitis
  • Ulcerative colitis or autoimmune liver conditions, which can give a p-ANCA pattern that is not always caused by MPO antibodies
  • Other autoimmune conditions, such as drug-induced lupus
  • ANCA-associated vasculitis, most often microscopic polyangiitis or eosinophilic granulomatosis with polyangiitis

What can help

  • Ask whether the result should be checked with a second test, such as the ANCA microscope test
  • Ask whether kidney function and urine tests make sense for your symptoms
  • Ask whether any of your medicines could be linked to this result
  • Keep track of symptoms such as blood in the urine, a long-lasting stuffy or bloody nose, a cough that will not clear, numbness or a new rash, 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
  • Medicines and infections 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.
  • Some medicines (hydralazine, minocycline, propylthiouracil) and cocaine mixed with levamisole can cause positive ANCA results.
  • Infection of the heart valves (infective endocarditis) can cause positive ANCA results.

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 blood or foam in your urine, a cough that will not go away, a long-lasting bloody or crusted nose, new numbness or weakness, or a new rash with fever or tiredness. 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 any of my medicines, or an infection, explain this result?
  • Which specialist should I see next?

Questions people ask

Does a positive MPO-ANCA mean I have vasculitis?

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. Some medicines, infections and bowel or liver 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. If suspicion stays high, your clinician may add the ANCA microscope test or look at other results.

Is this the same as the MPO test on a heart-risk panel?

No. This test looks for antibodies against MPO. The heart-risk MPO test measures the amount of the MPO protein itself, and the two answer different questions.

Show the science and sources

For clinicians and researchers

MPO-ANCA are IgG autoantibodies to myeloperoxidase, an enzyme in neutrophil granules. On ethanol-fixed neutrophils they usually give a perinuclear (p-ANCA) pattern, which Mayo describes as an artefact of fixation. Mayo notes that patients with GPA frequently have PR3 antibodies, while people with MPA or EGPA are more likely to have MPO antibodies, and ARUP reports that about 90% of people with a p-ANCA pattern by IFA have MPO specificity (Labcorp states at least 60%). 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 the EUVAS multicentre study found AUCs of 0.936 to 0.959 for most immunoassays against 0.843 and 0.923 for the two IFA methods (Damoiseaux 2017). In the 2022 ACR/EULAR classification criteria, p-ANCA or anti-MPO positivity scores +6 for MPA and -1 for GPA. 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 3.5 U/mL negative, 3.5 to 5.0 equivocal, above 5.0 positive. Mayo cautions that a positive result is not diagnostic, a negative result does not exclude AAV, and serial MPO-ANCA levels should not be relied on exclusively to judge response or flare risk. Positives without vasculitis include drug-associated ANCA (hydralazine, minocycline, propylthiouracil, levamisole-adulterated cocaine), infective endocarditis (a systematic review found ANCA in 18% to 43% of patients with endocarditis, most often with a c-ANCA/PR3 pattern), inflammatory bowel disease and autoimmune liver disease. This marker is not the plasma MPO mass measurement used in cardiovascular risk panels.

LOINC 46266-3 (primary), 6969-0, 48404-8, 97996-3, 29643-4, 17316-1. Specimen: serum.

Sources

  1. Myeloperoxidase (MPO) Antibody (test 0050526), ARUP Laboratories
  2. Myeloperoxidase Antibody (MPO) (test 8796), Quest Diagnostics
  3. Myeloperoxidase Antibodies, IgG, Serum (test MPO), Mayo Clinic Laboratories
  4. Antimyeloperoxidase (MPO) Antibodies (test 163059), Labcorp
  5. MPO/PR3 (ANCA) Antibodies (test 0050707), ARUP Laboratories
  6. Position paper: Revised 2017 international consensus on testing of ANCAs in granulomatosis with polyangiitis and microscopic polyangiitis, Nature Reviews Rheumatology (2017)
  7. 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)
  8. 2022 American College of Rheumatology/European Alliance of Associations for Rheumatology classification criteria for microscopic polyangiitis, Annals of the Rheumatic Diseases (ACR/EULAR) (2022)
  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. Antineutrophil Cytoplasmic Antibodies (ANCA) Test, MedlinePlus (U.S. National Library of Medicine)
  11. Trojan horses: drug culprits associated with antineutrophil cytoplasmic autoantibody (ANCA) vasculitis, Current Opinion in Rheumatology (2014)
  12. 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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