Vitamins and nutrition . Patient guide
Methylmalonic Acid (MMA) Blood Test
What is MMA
Methylmalonic acid is a metabolic intermediate that builds up in the blood when vitamin B12 is functionally deficient at cellular level. BSH 2014 guidance describes MMA as a useful, more specific second-line test to confirm cobalamin deficiency when serum B12 is borderline or the clinical picture is suggestive.
This biomarker entry is being clinically reviewed by our team. The factual content draws on UK guidance (NICE, NHS, Royal Colleges and the relevant speciality society where cited).
Reference range
Reported in µmol/L. Final reports always carry the issuing laboratory's range, which is what your clinician will interpret against.
| Group | Range | Note |
|---|---|---|
| Typical adult range | under 0.40 | µmol/L |
| Suggests functional B12 deficiency | 0.40 to 0.75 | |
| Confirms B12 deficiency | over 0.75 |
What it is
B12 is a cofactor for the enzyme methylmalonyl-CoA mutase. When intracellular B12 falls below functional level, that enzyme step stalls and methylmalonic acid accumulates in the blood and urine. MMA therefore reflects cellular B12 status, while a serum B12 reflects only what is in circulation.
Why a clinician would order it
MMA is the confirmatory test when a serum B12 is borderline or low but the clinical picture (sore tongue, neurological symptoms, hair shedding, fatigue) is suggestive. It is particularly useful in older patients, vegans, and anyone on metformin, proton pump inhibitors, or H2 blockers (all of which reduce B12 absorption without always dropping serum B12 below the lab reference).
If your level is outside the range
Symptoms of low MMA
- No symptoms attributable to low MMA
What low can indicate. Adequate cellular B12 status.
Symptoms of high MMA
- Symptoms relate to the underlying B12 deficiency: fatigue, hair shedding, paraesthesia, balance disturbance, sore tongue, low mood
What high can indicate. Functional B12 deficiency, even with a serum B12 in the lab "normal" range. Rarely raised in renal impairment without B12 deficiency, so kidney function should be considered when interpreting.
Testing tips
No fasting required. Hold B12 supplements and injections for at least one week before testing for a true baseline (MMA falls within days of starting B12 replacement). Always test alongside serum B12, folate, and homocysteine for the full picture.
Where you can get this tested
Methylmalonic Acid is not part of a standard WMG Health panel, but it can be added to one. Build a custom panel and our clinicians will confirm the markers and price in writing before you book.
Looking to book a test?
Comprehensive private health screening
Full blood screening at 134 Harley Street, London, reviewed by GMC-registered doctors with a written interpretation.
Sources
UK guidance our clinicians use when interpreting this marker.
This page is general patient information, not personal medical advice. A GMC-registered clinician will review your results and tailor any interpretation to you. See our Editorial Policy for how we write and review content.
Common questions about MMA
What is a normal MMA range?
Typical adult range: under 0.40 (µmol/L). Suggests functional B12 deficiency: 0.40 to 0.75. Confirms B12 deficiency: over 0.75. Always interpret your own results against the laboratory range printed on your report, since assay-specific reference ranges vary.
What does a low MMA result mean?
Adequate cellular B12 status.
What does a high MMA result mean?
Functional B12 deficiency, even with a serum B12 in the lab "normal" range. Rarely raised in renal impairment without B12 deficiency, so kidney function should be considered when interpreting.
Do I need to fast or prepare for the MMA blood test?
No fasting required. Hold B12 supplements and injections for at least one week before testing for a true baseline (MMA falls within days of starting B12 replacement). Always test alongside serum B12, folate, and homocysteine for the full picture.
Can I order a MMA blood test privately in London?
Yes. WMG Health offers MMA as part of a custom panel at our 134 Harley Street clinic. Results are released as each marker is reviewed, and the completion date is set by the slowest marker in your panel. We confirm the expected timeframe at booking. Book a standard panel online, or ask for a custom panel via /contact/ or 020 3239 3378.