Methylmalonic acid (MMA)
Also called: Methylmalonic acid, MMA
A sensitive tie-breaker for vitamin B12 deficiency. When a B12 level is borderline and it's unclear whether the body is truly short, a raised MMA confirms real deficiency at the tissue level — because B12 is needed to keep MMA low.
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What does Methylmalonic acid (MMA) measure?
Methylmalonic acid is a substance that the body can only clear with the help of vitamin B12. When B12 is genuinely lacking inside cells, MMA builds up — so a raised MMA is a sensitive, specific sign of true B12 deficiency, often before the standard blood B12 level looks clearly low. Its value is as a confirmatory test: the routine serum B12 has a grey zone where results are borderline and don't reliably say whether tissues are actually deprived. In that situation MMA (often with homocysteine) settles the question — a normal MMA makes significant B12 deficiency unlikely, while a raised MMA supports it and justifies treatment. Unlike homocysteine, MMA is specific to B12 and is not raised by folate deficiency, which helps separate the two.
What does a high Methylmalonic acid (MMA) level mean?
- True vitamin B12 deficiency — the main reason; confirms a tissue-level deficiency when the serum B12 is borderline.
- Kidney impairment — reduces MMA clearance and can raise it independently of B12.
- Rare inherited metabolic disorders (methylmalonic acidaemia) — very high levels, usually diagnosed in childhood.
What does a low Methylmalonic acid (MMA) level mean?
- Normal / not raised — makes significant B12 deficiency unlikely; a reassuring result when a borderline B12 needed clarifying.
When to discuss with a doctor
MMA is a second-line, confirmatory test rather than a routine one. It earns its place when a serum B12 sits in the borderline zone and the clinical question — is this person truly B12 deficient? — needs settling, especially with suggestive symptoms (fatigue, tingling, a macrocytic anaemia) or in vegans, older adults and those with absorption problems. A raised MMA (with a normal kidney function) supports genuine deficiency and treatment, while a normal MMA is reassuring. Mediora.AI shows MMA alongside B12, folate and the red-cell size so the deficiency question is read together; the treatment decision belongs with your doctor.
Related markers
Commonly confused with
- Vitamin B12 (Cobalamin) MMA is the confirming test, not an alternative one. B12 in the blood can look normal while the cells are already short of it; MMA rises in exactly that case, which is why it is ordered when the B12 result is borderline.