Anti-Mitochondrial M2 Antibody

Antibodies against the M2 part of mitochondria, measured by ELISA. They are strongly linked to primary biliary cholangitis, a chronic bile duct condition of the liver.

AI-drafted. Awaiting verificationAlso called AMA-M2LOINC 49781-8

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What it is

Mitochondria are the parts of your cells that make energy. The M2 antigen is a group of enzymes inside them, and anti-M2 antibodies are the form of anti-mitochondrial antibody (AMA) that most tests look for. This ELISA gives a number rather than a dilution (titer), but each kit has its own scale and cutoff. Some labs print it as positive or negative only.

Why it matters

Anti-M2 antibodies are found in most people with primary biliary cholangitis (PBC), a long-term condition in which the small bile ducts in the liver are slowly damaged. When liver blood tests point to the bile ducts, a clearly positive result is usually enough for clinicians to confirm PBC without a liver biopsy. A low result in someone with normal liver tests is less specific, and a negative result does not rule PBC out.

If it’s high

A result above your lab's cutoff is reported as positive. It is strongly linked to PBC, but it is read together with liver blood tests such as ALP. A positive result in someone with normal liver tests is less clear. In older studies many such people went on to develop signs of PBC over many years, usually without advanced liver disease, so clinicians commonly recheck liver tests over time.

Common causes

A weak or borderline result with normal liver blood tests, which is less specific and whose meaning is still being studied
Primary biliary cholangitis, the main condition linked to anti-M2 antibodies
Another autoimmune condition, such as systemic sclerosis, where AMA have been reported in some studies

What can help

Ask whether your liver blood tests, especially ALP, are normal and how often they should be rechecked
Ask whether other PBC-related antibodies, such as anti-gp210 or anti-sp100, would add information
Tell your clinician about itching, unusual tiredness, or yellowing of the skin or eyes

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: 0–20 Units. Source: ARUP Laboratories, UI Health Care (University of Iowa Hospitals & Clinics) Laboratory Services Handbook.

Adults (this one applies)0–20 Units
Sources: ARUP Laboratories, UI Health Care (University of Iowa Hospitals & Clinics) Laboratory Services Handbook

What can affect your result

Test kit: each ELISA has its own scale and cutoff
Method: ELISA can be more sensitive than immunofluorescence, but no single method finds every person with PBC
Treatment for PBC can lower the level
Liver blood tests: the same result means different things when ALP is normal and when it is raised
Different ELISA kits use their own scales and cutoffs, so results are not interchangeable between labs.
ARUP rejects plasma and samples that are contaminated, hemolyzed, very yellow (icteric) or very fatty (lipemic) for this test.
Treatment for primary biliary cholangitis can lower the level.

When to talk to a clinician

A positive anti-M2 result is not urgent by itself. Talk with a clinician about it, especially if you have persistent itching, unusual tiredness, yellowing of the skin or eyes, or raised liver blood tests. If your liver tests are normal, a common approach is to recheck them once a year.

Questions you could ask

Does this result matter for any other autoimmune condition I have?
What do my liver blood tests, especially ALP, show?
Would other PBC-related antibody tests add information?
How often should my liver tests be rechecked?

Questions people ask

What is the difference between AMA and anti-M2?

AMA is the general name for antibodies against mitochondria, and some labs measure it by immunofluorescence and report a titer. Anti-M2 is a more specific ELISA that targets the M2 part and gives a number. Both point toward primary biliary cholangitis.

Does a positive result mean I have a liver disease?

Not always. The antibody is strongly linked to primary biliary cholangitis, but the result is read with liver blood tests. A weak positive with normal liver tests is usually followed with regular liver blood tests rather than a biopsy or treatment, according to a UK guideline.

Can I have PBC with a negative result?

Yes. Most, but not all, people with PBC have these antibodies. Others have different PBC-related antibodies, such as anti-gp210 or anti-sp100, and a few are diagnosed by biopsy.

Show the science and sources

For clinicians and researchers

Anti-M2 antibodies target the E2 subunits of the 2-oxo-acid dehydrogenase complexes in the inner mitochondrial membrane, chiefly the E2 component of the pyruvate dehydrogenase complex (BSG/UK-PBC 2018). ELISA, immunoblot and multiplex immunoassays for M2 are widely used, alongside or instead of AMA by immunofluorescence. The BSG guideline notes that no approach is clearly superior, that ELISA can be more sensitive and less prone to non-specific reactivity from the raised polyclonal IgM of PBC, and that a titer above 1:40 is conventionally positive for immunofluorescence (kit cutoffs for ELISA are set by the manufacturer). It states that AMA in the right context of cholestatic liver tests is usually sufficient to diagnose PBC without biopsy (strong recommendation, high-quality evidence). It also finds no evidence that the concentration above the diagnostic threshold has prognostic value, advises against repeating the test once PBC is established, and notes the level can fall on ursodeoxycholic acid. Pooled sensitivity and specificity for the M2 subtype were 89% (95% CI 81-94%) and 96% (93-98%) in a 2023 meta-analysis of 16 studies, compared with 84% and 98% for AMA by all methods. ARUP quotes AMA in 90-95% of people with PBC, notes that lower sensitivities have been reported depending on cohort and assay, and that some patients are positive for anti-sp100 or anti-gp210 instead (and that a negative result does not rule PBC out). ARUP reports its ELISA in arbitrary Units: 20.0 or less negative, 20.1 to 24.9 equivocal, 25.0 or more positive. Other kits use a different scale under the same unit name: University of Iowa Hospitals reports negative below 0.1 Units and positive 1.0 or more. Other kits use a different scale under the same unit name: University of Iowa Hospitals reports negative below 0.1 Units and positive 1.0 or more.

LOINC 49781-8 (primary), 14251-3, 51715-1, 26054-7. Specimen: serum.

Sources

Mitochondrial M2 Antibody, IgG (ELISA) (test 0050065), ARUP Laboratories
The British Society of Gastroenterology/UK-PBC primary biliary cholangitis treatment and management guidelines, Gut (2018)
Diagnostic value of anti-mitochondrial antibody in patients with primary biliary cholangitis: A systemic review and meta-analysis, Medicine (Baltimore) (2023)
Primary Biliary Cholangitis, ARUP Consult
Mitochondrial Antibodies (M2), UI Health Care (University of Iowa Hospitals & Clinics) Laboratory Services Handbook

AI-drafted. Awaiting verification. Last reviewed 2026-10-03. How we build and check these pages.