The essentials

Methylmalonic acid (MMA) builds up in the blood when cells lack usable vitamin B12. Doctors order it mainly when a B12 result falls in the gray zone, to confirm or rule out a deficiency. A high MMA usually means low B12, but kidney problems and age can also raise it, so read it with B12, homocysteine and creatinine.

How do I read my methylmalonic acid result?

A fictitious US example where the B12 level alone left doubt:

Fictitious example of B12 follow-up report lines (United States format)
TestResultReference rangeFlag
Vitamin B12262 pg/mL232-1245 pg/mL-
Methylmalonic Acid, Serum512 nmol/L0-378 nmol/LH
Homocysteine16.8 µmol/L0.0-14.5 µmol/LH
Creatinine0.86 mg/dL0.57-1.00 mg/dL-
  1. Vitamin B12: in range, but in the zone UK guidelines call indeterminate (180 to 350 ng/L, same as pg/mL)[5]. That is why MMA was added.
  2. Methylmalonic acid: above the 378 nmol/L limit of a large US lab[4]. This line points to cells that are short of B12.
  3. Homocysteine: upper limit for adults 18 to 60 at the same lab[12]. It rises with a lack of B12 or of folate[6].
  4. Creatinine: normal, so the kidneys are unlikely to explain the high MMA[6].

A borderline B12 and a flagged MMA? BloodSense reads every line of your report together, kidney and blood count included, and helps you prepare questions for your doctor.

Get my MMA result explained

For the B12 number itself (ranges, units, low or high), see our guide to vitamin B12 blood levels.

What is a methylmalonic acid test used for?

An MMA test is most often used to diagnose vitamin B12 deficiency[1]. Cells need B12 to turn methylmalonyl-CoA into succinyl-CoA; without it, MMA builds up in blood and urine[6]. MMA shows how cells use B12, not just how much circulates. It helps in three situations:

  • A gray-zone B12 result with symptoms. UK guidelines (NICE) advise serum MMA when symptoms fit and total or active B12 is indeterminate[5].
  • Suspected deficiency from recreational nitrous oxide. NICE advises MMA or homocysteine as the first test[5].
  • Follow-up when symptoms do not improve on treatment[5].

In babies, newborn screening looks for methylmalonic acidemia, a rare inherited disorder[1].

What is the normal range for methylmalonic acid?

US labs use nmol/L; some use µmol/L (1 µmol/L = 1,000 nmol/L).

Serum methylmalonic acid reference values
Age or settingReference valueSource
Single range, no age bands0 to 378 nmol/LLabcorp (United States)[4]
2 to 59 years55 to 335 nmol/LQuest Diagnostics (United States)[3]
60 to 79 years69 to 390 nmol/LQuest Diagnostics (United States)[3]
80 years and older85 to 423 nmol/LQuest Diagnostics (United States)[3]
General range0.07 to 0.27 µmol/L (70 to 270 nmol/L)MedlinePlus, US National Library of Medicine[2]
Usual cut-off for "elevated"About 370 nmol/LLabcorp (United States)[4]

The upper limit rises with age. Your laboratory's range, printed next to your result, is the one that applies[5].

How do B12, MMA, homocysteine and active B12 fit together?

Four markers describe B12 status: total B12, active B12 (holotranscobalamin), homocysteine and MMA[6]. Only B12 clears MMA, which makes it the most specific. Homocysteine levels also rise when folate is low[6].

Common combinations and what they usually suggest
PatternUsual reading
B12 low or borderline, MMA ↑, homocysteine ↑B12 deficiency likely[6]
B12 borderline, MMA normal, homocysteine normalB12 deficiency unlikely; look for another cause of symptoms[5]
MMA normal, homocysteine ↑Think of low folate, among other causes[6]
MMA ↑ with normal or high B12 and raised creatinineKidney function may explain MMA; active B12 helps decide[6]
Active B12 below 25 pmol/LDeficiency confirmed; 25 to 70 pmol/L is indeterminate[5]

In 316 people with cancer, B12 and MMA were only weakly linked, and MMA best predicted deficiency[8]: one number is rarely enough. For folate, see our folic acid blood test guide.

What causes high methylmalonic acid?

  • Common Vitamin B12 deficiency, from diet, poor absorption (autoimmune gastritis, celiac disease, stomach or bowel surgery) or medicines[5]. MMA often rises at an early stage[4].
  • Common Reduced kidney function. MMA can be high without any B12 shortage[6]. In US data on 18,569 people, MMA was about 36% higher in the top quarter of creatinine than in the bottom one[7]; check your eGFR result.
  • Common Older age. MMA was about 63% higher after 70 than at 21 to 30 years (197 vs 121 nmol/L), partly from falling kidney function and B12 status[7].
  • Possible Metformin. After 13 years in a US trial, low or borderline B12 affected 20.3% on metformin vs 15.6% on placebo[9], a common diabetes medicine.
  • Possible Acid-reducing medicines. Two years or more of proton pump inhibitors (PPIs), often used for acid reflux, carried 1.65 times the odds of B12 deficiency[10].
  • Possible Recreational nitrous oxide, a recognized cause of B12 deficiency[5].
  • Rare Methylmalonic acidemia, an inherited disorder in about 1 in 50,000 to 100,000 people, usually seen in early infancy[11].

Untreated, B12 deficiency causes anemia, visible on a complete blood count, and nerve damage[6]. MMA does not measure severity[1].

What does a normal or low MMA mean?

With normal kidneys, a normal MMA makes a B12 shortage unlikely: it is the most sensitive and specific B12 marker[6]. If symptoms persist, other causes are looked for[5]. A low MMA is uncommon and not a health problem[1].

An MTHFR mutation test concerns folate and homocysteine, not MMA[6].

What can skew a methylmalonic acid result?

  • Have blood taken before starting B12 tablets or injections, as guidelines advise[5].
  • Tell the lab about any over-the-counter B12 product, including patches[5].
  • Ask whether to fast: some labs ask for several hours, others have no rule[1][3].
  • Have a recent creatinine or eGFR on file: kidney function changes the reading[6].
  • The serum must be separated from cells within one hour[4].
  • Compare results from the same lab and unit (nmol/L or µmol/L).

See also what to expect at a blood draw.

When should I see a doctor about a high MMA?

When to see a doctor

  • Emergency: call 911 for sudden weakness, trouble speaking or new confusion.
  • Within 24 to 48 hours if a high MMA comes with tingling feet, unsteadiness or a low hemoglobin. Doctors may start B12 treatment before MMA returns[5]. For an abnormal newborn screen, call the pediatrician the same day.
  • At your next appointment if you feel well and MMA is slightly high.

Questions to ask your doctor

  1. Was my B12 in the gray zone, and does my MMA confirm a deficiency?
  2. Could my kidney function or age explain this MMA?
  3. Could metformin or an acid-reducing medicine be involved?
  4. Should we also check active B12, folate or intrinsic factor antibodies?

Frequently asked questions

Can MMA be measured in urine?

Yes, in a random sample or a 24-hour collection[1]. Adult guidelines refer to serum MMA[5], so blood is more common.

Can MMA be high when B12 is high?

Yes. In one study, 15 to 30% of people with a high serum B12 also had a high MMA, often reflecting kidney problems rather than true deficiency[6].

Can B12 be deficient with a normal B12 level?

Yes. A shortage inside cells has been documented with normal and even high serum B12[6].

  1. MedlinePlus. Methylmalonic Acid (MMA) Test. US National Library of Medicine; updated June 10, 2024. medlineplus.gov (accessed November 8, 2026)
  2. MedlinePlus Medical Encyclopedia. Methylmalonic acid blood test. US National Library of Medicine; reviewed October 1, 2025. medlineplus.gov (accessed November 8, 2026)
  3. Quest Diagnostics. Methylmalonic Acid (test code 34879). testdirectory.questdiagnostics.com (accessed November 8, 2026)
  4. Labcorp. Methylmalonic Acid, Serum or Plasma (test 706961). labcorp.com (accessed November 8, 2026)
  5. National Institute for Health and Care Excellence. Vitamin B12 deficiency in over 16s: diagnosis and management (NG239). March 6, 2024. nice.org.uk (accessed November 8, 2026)
  6. Hannibal L, Lysne V, Bjørke-Monsen AL, et al. Biomarkers and algorithms for the diagnosis of vitamin B12 deficiency. Front Mol Biosci. 2016;3:27. doi:10.3389/fmolb.2016.00027 (accessed November 8, 2026)
  7. Ganji V, Kafai MR. Population reference values for serum methylmalonic acid concentrations and its relationship with age, sex, race-ethnicity, supplement use, kidney function and serum vitamin B12 in the post-folic acid fortification period. Nutrients. 2018;10(1):74. doi:10.3390/nu10010074 (accessed November 8, 2026)
  8. Vashi P, Edwin P, Popiel B, Lammersfeld C, Gupta D. Methylmalonic acid and homocysteine as indicators of vitamin B-12 deficiency in cancer. PLoS One. 2016;11(1):e0147843. doi:10.1371/journal.pone.0147843 (accessed November 8, 2026)
  9. Aroda VR, Edelstein SL, Goldberg RB, et al. Long-term metformin use and vitamin B12 deficiency in the Diabetes Prevention Program Outcomes Study. J Clin Endocrinol Metab. 2016;101(4):1754-1761. doi:10.1210/jc.2015-3754 (accessed November 8, 2026)
  10. Lam JR, Schneider JL, Zhao W, Corley DA. Proton pump inhibitor and histamine 2 receptor antagonist use and vitamin B12 deficiency. JAMA. 2013;310(22):2435-2442. doi:10.1001/jama.2013.280490 (accessed November 8, 2026)
  11. MedlinePlus Genetics. Methylmalonic acidemia. US National Library of Medicine. medlineplus.gov (accessed November 8, 2026)
  12. Labcorp. Homocyst(e)ine (test 706994). labcorp.com (accessed November 8, 2026)

This page is general information. It does not replace the advice of a doctor, who interprets your results with your symptoms, history and examination.