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Methylmalonic Acid (MMA), Serum

Measures methylmalonic acid, a substance that builds up in your blood when your cells do not get enough usable vitamin B12.

AI-drafted. Awaiting verificationLOINC 13964-2

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What it is

Your body makes a small amount of methylmalonic acid (MMA) when it breaks down certain fats and proteins. An enzyme that needs vitamin B12 normally clears it away. When there is not enough usable B12 inside your cells, MMA backs up and rises in the blood. Because MMA reflects what B12 is doing inside cells, it can be useful when a regular B12 blood level lands in the gray zone.

Why it matters

A B12 level on its own can miss a real shortage, especially when it is borderline. MMA is a more specific signal of low B12 and is often checked along with B12, homocysteine or active B12 (holotranscobalamin). Kidney function, age and some gut conditions also change MMA, so it is read together with your other results. In babies, a high MMA can occasionally point to a rare inherited condition, so it is followed up by the clinician who ordered the test.

If it’s low

A low MMA is not considered a health problem. It is usually just a normal result, or it can follow recent B12 supplements or injections.

Common causes

  • Normal variation between people
  • Recent vitamin B12 supplements or injections
  • Younger age, since MMA tends to be lower in younger adults

If it’s high

A high MMA is most often linked to low vitamin B12 status, but it can also rise for other reasons, including reduced kidney function and older age. A modest rise is common. Your clinician can put it in context with your B12, homocysteine, kidney tests and symptoms.

Common causes

  • Low vitamin B12 intake or poor absorption, for example from a vegan diet, pernicious anemia, stomach or bowel surgery or disease, or some long-term medicines
  • Reduced kidney function
  • Older age, since MMA rises with age even when B12 is replete
  • Dehydration (low blood volume)
  • Overgrowth of bacteria in the small intestine
  • In infants and children, inherited conditions of B12 or MMA handling

What can help

  • Ask your clinician whether your B12, homocysteine, active B12 or kidney function should be checked too
  • Ask your clinician about the likely cause and whether B12 treatment makes sense for you
  • Eat B12-rich foods such as meat, fish, eggs, dairy or fortified foods

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.

The usual range depends on age. Choose an age to see the one that applies.

Children and teens 4 ranges

See Serum MMA by age and sex, with the U.S. survey numbers where they exist.

If this applies to you

Serum MMA means a little more for some people. Open the one that fits you.

Age 65 or older

When a B12 result is borderline, a 2025 American Family Physician review suggests an MMA test as the next step, to help show whether the body is short of B12.

Blood tests for older adults

Vegan or vegetarian

MMA builds up when cells don't get enough usable B12. The Academy lists it with serum B12 and holotranscobalamin as the lab tests for B12 status, and a review of B12 in vegetarians found such functional markers give more detail than B12 alone.

Blood tests on a vegan or vegetarian diet

What can affect your result

  • Vitamin B12 status
  • Kidney function
  • Age: MMA rises with age, especially after about 70, even in people with enough B12 and normal kidneys
  • How recently you ate: a shorter fast was linked to about 10% higher MMA in US survey data
  • Vitamin B12 supplements and treatment, which lower MMA
  • Reduced kidney function raises MMA even when vitamin B12 is fine. In US survey data, impaired kidney function was linked to roughly 50% to 70% higher MMA.
  • Eating shortly before the draw can raise MMA a little (about 10% higher with a shorter fast in US survey data). Quest says fasting is not required, but MedlinePlus says you may need to fast, so follow your lab's instructions.
  • Vitamin B12 supplements or injections lower MMA, and MMA can fall within days of starting treatment, so a result after treatment does not show your earlier status.

Any time of day. MMA can start to fall within days of starting vitamin B12 treatment. One 2026 review reports it normalizing within the first 5 days unless kidney function is reduced, in which case it may stay raised longer.

When to talk to a clinician

Talk with a clinician soon if a high MMA comes with numbness or tingling in the hands or feet, trouble walking or balance, memory or mood changes, a sore smooth tongue or unusual tiredness. For infants and children, a markedly high MMA is followed up promptly by the clinician who ordered the test.

Questions you could ask

  • Should this be rechecked after treatment or a change in my diet, and when?
  • Could low vitamin B12 or my kidney function explain this result?
  • Should we check homocysteine or active B12 (holotranscobalamin) as well?

Questions people ask

Does a high MMA mean I have a B12 deficiency?

Not necessarily. A high MMA suggests that your cells may not be getting enough usable B12, but kidney function, age and other conditions also raise it. Clinicians read it together with your B12, homocysteine and kidney tests.

Why is the normal range different at my lab?

Labs set ranges from different groups of people and use different units. Quest's range for most adults is 55 to 335 nmol/L, and it is higher in older age groups. Some labs report in µmol/L or nmol/mL instead, so check the unit as well as the numbers. Use the range printed on your own report.

How do I convert between units?

1 µmol/L is the same as 1 nmol/mL and equals 1,000 nmol/L. So 0.30 µmol/L is 300 nmol/L.

Show the science and sources

Units

  • 1 nmol/L = 1 nmol/L
  • 1 nmol/L = 0.001 µmol/L
  • 1 nmol/L = 0.001 nmol/mL

Open the Serum MMA unit converter

Is a change real?

Serum MMA naturally varies about 7.2% from test to test in the same healthy person. Between two results from the same lab, a change of roughly 22% or more is unlikely to be day-to-day noise or lab variation (95% reference change value). Source: Week-to-week biological variation of methylmalonic acid and homocysteine in healthy women (Lindberg M et al.).

For clinicians and researchers

MMA is the free acid that accumulates when adenosylcobalamin-dependent methylmalonyl-CoA mutase is impaired, and is measured by isotope-dilution LC-MS/MS (NHANES uses butanol derivatization). Quest reports in nmol/L; other labs may report µmol/L or nmol/mL (numerically equal to µmol/L). Reference intervals differ by lab and by age: Quest lists 55-335 nmol/L for ages 2 to 59 rising to 85-423 at 80 and older. In NHANES 2011-2014, the central 95% interval was 70.6-451 nmol/L in all US adults but narrowed to 63.5-254 (20-39 y), 70.5-293 (40-59), 72.4-281 (60-69) and 84.3-317 (70 and older) in adults with serum B12 of at least 300 pmol/L and normal kidney function, which supports age-specific limits and shows how much the choice of reference group matters. Elevation thresholds in the literature range from about 260 to 350 nmol/L. Impaired renal function (50% to 70% higher) and a shorter fast (about 10% higher) raise MMA, while B12 supplement use was associated with about 5% lower values. Normalization after B12 replacement is usually rapid unless kidney function is reduced. Serum MMA is distinct from urine MMA, which is used for inherited disorders, and from monomethylarsonic acid, an arsenic metabolite also abbreviated MMA.

LOINC 13964-2 (primary), 2629-4. Specimen: serum-or-plasma.

Sources

  1. Methylmalonic Acid (test 34879), Quest Diagnostics
  2. Age-specific reference ranges are needed to interpret serum methylmalonic acid concentrations in the US population, American Journal of Clinical Nutrition (2019)
  3. Biomarkers and Algorithms for the Diagnosis of Vitamin B12 Deficiency, Frontiers in Molecular Biosciences (2016)
  4. Methylmalonic Acid (MMA) Test, MedlinePlus (National Library of Medicine)
  5. Revisiting the hematological manifestations of vitamin B12 deficiency, Frontiers in Nutrition (2026)

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

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