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Methylmalonic Acid (MMA)

Methylmalonic acid (MMA) is a metabolite that builds up when your cells run short on vitamin B12.

What is Methylmalonic Acid (MMA)?

Methylmalonic acid (MMA) is a substance that builds up as soon as your cells run short on active vitamin B12. B12 is needed to break MMA down further — when it is lacking, MMA accumulates and the blood level rises. That makes MMA a functional measure: it shows whether your B12 is genuinely doing its job inside the cells, not just how much sits in your blood. MMA rises specifically with a B12 deficiency, whereas homocysteine also rises with other vitamin shortfalls. That specificity makes MMA valuable when your B12 value falls in the grey zone.

Why is Methylmalonic Acid (MMA) relevant?

A standard B12 blood test can mislead: the blood sometimes shows B12 that your cells cannot actually use. MMA cuts through that by measuring whether the B12 is doing its work. That makes it most useful when your B12 value is borderline. MMA is especially relevant with symptoms that fit a B12 deficiency — unexplained fatigue, tingling, or a form of anaemia — while the ordinary B12 value still looks normal. For at-risk groups such as older adults, vegans, and long-term metformin users, it is a logical complement.

Methylmalonic Acid (MMA) high or low — what it means

Read MMA together with your B12 value and homocysteine. A raised MMA and raised homocysteine with a low or borderline B12 points to a B12 deficiency at the cellular level. A raised homocysteine with a normal MMA fits more with a folate deficiency. Your kidney function is a key confounder: with reduced eGFR, MMA rises even without a B12 deficiency. So always check your creatinine and eGFR when interpreting it. After starting B12 supplementation, a repeat after 4–8 weeks is useful; if MMA does not fall, absorption problems or another cause are worth investigating.

Methylmalonic Acid (MMA) reference ranges

NormalCut-off used by Saltro/Unilabs (the Optimize lab): below this a vitamin B12 deficiency is very unlikely.< 0.35 µmol/L
ElevatedA cellular vitamin B12 deficiency is likely; weigh together with B12, homocysteine and kidney function.≥ 0.35 µmol/L
Treatment threshold with symptomsMost commonly used literature threshold to treat when matching B12 symptoms are present (Stichting B12 Tekort).> 0.27 µmol/L

Cut-offs vary considerably by lab and method: in the Netherlands reference values range from < 0.31 µmol/L (VUmc Amsterdam) to < 0.45 µmol/L (Erasmus MC Rotterdam); the Optimize lab (Saltro/Unilabs) uses < 0.35 µmol/L. Reduced kidney function can falsely raise MMA. Not a diagnosis — always read alongside B12 and homocysteine, and the value on your own lab report is leading.

Educational information only — not medical advice. Consult a healthcare professional for clinical decisions.

Read about our scientific approach →Read the guide: Energy →

Frequently asked questions

What is a normal methylmalonic acid (MMA) level?

At the Optimize lab a normal MMA sits below 0.35 µmol/L; below that a cellular vitamin B12 deficiency is very unlikely. The exact limit differs by lab (in the Netherlands from < 0.31 µmol/L to < 0.45 µmol/L), so always compare your value with the reference interval printed on your own result.

What does a high MMA level mean?

An MMA of 0.35 µmol/L or higher makes a cellular vitamin B12 deficiency likely — even when your ordinary B12 blood level still looks 'normal'. In the literature, treatment is already considered from 0.27 µmol/L if matching symptoms are present. Note: reduced kidney function can also falsely raise MMA, so it is always assessed together with B12, homocysteine and your kidney values (creatinine/eGFR).

Can MMA be too low?

A low MMA is not a problem — the lower it is, the more reassuring it is for your cellular B12 status. There is no 'too low' MMA to worry about; the marker exists precisely to detect an elevation.

When is a high MMA concerning and what can you do about it?

It is mainly concerning when a raised MMA goes together with symptoms that fit a B12 deficiency — fatigue, tingling or numbness in the arms/legs, or anaemia with large red blood cells. With a confirmed deficiency, MMA usually falls after starting B12 supplementation; a repeat test after a few weeks can confirm this. If MMA does not fall, or your kidney function is reduced, discuss this with your doctor for further work-up.

Related biomarkers

Folate (vitamin B9)
Folate is a B vitamin your body needs for DNA synthesis, cell division and blood production.
Homocysteine
Homocysteine is an amino acid your body clears with B-vitamins, rising when folate or B12 runs short.
Vitamin B12
Vitamin B12 is a B vitamin your body needs for your nerves, DNA production, and blood formation.

Methylmalonic Acid (MMA) is one of the biomarkers in the Optimize blood test. Book a blood draw at any of 238+ partner labs in the Netherlands, or upload your existing results in the app.

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