MMA Test: What It Shows About B12 and What Your Number Means
An MMA (methylmalonic acid) test can show low B12 even when your blood B12 looks normal. NIH says a level above 271 nmol/L suggests low B12. Some labs flag only higher values, so ask what your lab’s range means for you.
MMA builds up in your blood when your cells run short of B12. Doctors order the test when your blood B12 is borderline: under 200 pg/mL is low, and 200 to 300 is borderline (NIH). They also order it when you have signs of low B12, such as numbness or tingling, but a normal B12 result.
What your MMA number means
Check the unit first. Some labs report MMA in nmol/L and some in µmol/L. To change µmol/L to nmol/L, multiply by 1,000: 0.19 µmol/L is 190 nmol/L.
Your lab may call anything up to 378 nmol/L normal, as Labcorp does. NIH says low B12 becomes likely above 271.
| MMA (nmol/L) | What it usually means |
|---|---|
| 271 or lower | Normal. Low B12 is unlikely. |
| 272 to 378 | Suggests low B12 (NIH), though some labs still call it normal. |
| Above 378 | High by NIH’s line and Labcorp’s range. Low B12 is likely. |
What else can raise MMA
MMA also rises with weak kidneys and tends to run higher in older adults, so your doctor reads it with your kidney function in mind (NIH). Rare inherited disorders raise MMA too. They are mostly found in newborn screening (MedlinePlus).
How to prepare, and how long results take
You usually don’t need to fast. Labcorp gives no fasting instruction, but some providers ask you to fast for a few hours (MedlinePlus), so follow what you are told.
Tell your doctor if you take B12 pills or get shots. They can lower your result and hide low B12.
If you gave blood recently, your doctor can often add MMA to that sample. Labcorp says the sample keeps for 14 days. Results take 3 to 6 days at Labcorp.
If your MMA is high
Your doctor will look for the cause, such as diet, poor absorption or a medicine, and choose pills or shots. Pernicious anemia and nerve symptoms are usually treated with shots (NIH). Treatment brings MMA down fast. In one trial, it dropped back to normal within 4 months, by pill or by shot (Kuzminski 1998).
Pills, shots and what to expect are in B12 deficiency treatment.
If your doctor says to take a B12 pill
Your doctor sets the dose. The usual daily pill holds 1,000 mcg, the size on about 1 in 3 of the 203 B12 labels we read. If that is your dose, this is the one we would buy.
NatureWise Vitamin B12 1000 mcg
$0.12 a day. A softgel on NSF’s testing list. Contains gelatin.
If your doctor prefers methylcobalamin, Thorne Vitamin B12 is on two NSF testing lists.
If you are vegan, Jarrow Methyl B-12 is a lemon chewable labeled vegan.
Frequently asked questions
Is the MMA test part of a regular B12 test?
No. It is a separate blood test that your doctor orders by name. Labs may list it as “methylmalonic acid, serum” (Labcorp test 706961). MMA can also be measured in urine (MedlinePlus).
Is MMA better than a homocysteine or active B12 test?
Each has a weak spot. Homocysteine also rises when B12 is low, but low folate raises it too (NIH). Active B12 measures the part of blood B12 that cells can take up, and not every lab offers it. UK experts say no single test is a gold standard, and treatment should not wait when strong symptoms and a result disagree (Devalia 2014).
Can an MMA result be too low?
A result below the normal range is uncommon and is not a health problem (MedlinePlus).
Related guides
- Vitamin B12 guide: what B12 does and who needs more
- How much B12 per day: the daily amount by age and why pills hold 1,000 mcg
- B12 for vegans: why the regular B12 test can mislead vegans
- B12 for seniors: why low B12 is more common after 50
Sources
- NIH Office of Dietary Supplements. "Vitamin B12: Fact Sheet for Health Professionals" (MMA above 0.271 micromol/L; blood B12 cut-offs; kidneys and age; homocysteine). ods.od.nih.gov (updated July 2, 2025; read October 15, 2026).
- Labcorp. Methylmalonic Acid, Serum or Plasma, test 706961 (reference interval, sample stability, turnaround). labcorp.com (read October 16, 2026).
- MedlinePlus. Methylmalonic Acid (MMA) Test. medlineplus.gov
- Kuzminski AM, et al. "Effective treatment of cobalamin deficiency with oral cobalamin." Blood. 1998. PMID: 9694707
- Devalia V, Hamilton MS, Molloy AM. "Guidelines for the diagnosis and treatment of cobalamin and folate disorders." Br J Haematol. 2014. PMID: 24942828
- Prices are each brand’s list price, checked October 15, 2026. Amazon’s price may differ.