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This article waslast modified on 21 June 2023.
At a Glance
Why Get Tested?

Methylmalonic acid (MMA) is not often required; however, it may be useful in the following circumstances:

  • Detect early and/or mild Vitamin B12 deficiency, when vitamin B12 results are equivocal (they neither rule in nor rule out deficiency), and there is a high clinical suspicion of deficiency.
  • Diagnose/monitor patients with methylmalonic acidaemia, a rare inherited metabolic disorder. Early detection allows for prompt treatment, which can help prevent or minimise complications associated with the disorder.


When To Get Tested?

Sometimes MMA can be helpful when vitamin B12 concentration is at the low end of the normal range and patient appears symptomatic of vitamin B12 deficiency. These include:

  • Neuropathy, such as numbness and tingling in the hands and feet
  • Unexplained macrocytosis (large blood cells)


Sample Required?

A blood sample taken from a vein in your arm

Test Preparation Needed?

None required

On average it takes 7 working days for the blood test results to come back from the hospital, depending on the exact tests requested. Some specialist test results may take longer, if samples have to be sent to a reference (specialist) laboratory. The X-ray & scan results may take longer. If you are registered to use the online services of your local practice, you may be able to access your results online. Your GP practice will be able to provide specific details.

If the doctor wants to see you about the result(s), you will be offered an appointment. If you are concerned about your test results, you will need to arrange an appointment with your doctor so that all relevant information including age, ethnicity, health history, signs and symptoms, laboratory and other procedures (radiology, endoscopy, etc.), can be considered.

Lab Tests Online-UK is an educational website designed to provide patients and carers with information on laboratory tests used in medical care. We are not a laboratory and are unable to comment on an individual's health and treatment.

Reference ranges are dependent on many factors, including patient age, sex, sample population, and test method, and numeric test results can have different meanings in different laboratories.

For these reasons, you will not find reference ranges for the majority of tests described on this web site. The lab report containing your test results should include the relevant reference range for your test(s). Please consult your doctor or the laboratory that performed the test(s) to obtain the reference range if you do not have the lab report.

For more information on reference ranges, please read Reference Ranges and What They Mean.

What is being tested?

Vitamin B12 plays a crucial role in the conversion of methylmalonyl-CoA to succinyl-CoA, a step in the breakdown of certain amino acids and fatty acids. When vitamin B12 levels are low, the body's ability to convert methylmalonyl-CoA to succinyl-CoA is compromised, leading to an accumulation of MMA. As a result, measuring MMA in either urine or blood may be useful for assessing vitamin B12 deficiency.

Active B12 (metabolically active component of vitamin B12) may be used instead of MMA as a marker of vitamin B12 deficiency. Active B12 measurement provides a more direct assessment of the functional availability of vitamin B12 for cellular functions.

Increased production of MMA in newborn babies may suggest one of the inherited problems collectively known as methylmalonic acidaemias. Babies with this disease are unable to convert methylmalonyl CoA to succinyl CoA; therefore, increased production of MMA occurs.


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Common Questions
  • How is it used?

    MMA is primarily requested, sometimes along with homocysteine, to help diagnose vitamin B12 deficiency, when results of vitamin B12 analysis are equivocal.

    Vitamin B12 analysis is available routinely and in majority of cases will be sufficient to assess for deficiency. It is important to detect vitamin B12 deficiency as it can cause a decrease in the number of red blood cells (anaemia) and changes to bone marrow function. It can also cause peripheral neuropathy (damage to the nerves in the arms and legs, leading to numbness and tingling in the hands and feet), glossitis (inflammation of the tongue), and/or mental or behavioural changes (confusion, irritability, depression).

    Occasionally, MMA measurement may be requested to help diagnose methylmalonic acidaemia, a rare inherited metabolic disorder that occurs in about 1 in 50,000 to 100,000 people. Babies with this disease are unable to convert methylmalonyl CoA to succinyl CoA. They appear normal at birth but as they ingest protein, they begin to show symptoms such as seizures, failure to thrive, mental retardation, strokes, and severe metabolic acidosis. Often the presence of MMA will be assessed as part of a wider screen for inherited metabolic disorders.


  • When is it requested?

    MMA is not often required. Until there is more data supporting its use and consensus on its clinical utility and long-term benefits, it will probably not be routinely used by doctors.

    MMA may be requested, sometimes along with a homocysteine test, when a vitamin B12 result is equivocal, but there is a high suspicion of vitamin B12 deficiency in a patient, such as heavy recreational user of nitrous oxide. Nitrous oxide (laughing gas), a colourless gas commonly used as a painkiller, is increasingly being taken as a recreational drug. Intensive and frequent use of nitrous oxide inactivates vitamin B12, which means that vitamin B12 is not available to be utilised by the body. This can lead to a functional deficiency of vitamin B12, resulting in neurological damage, even if blood tests for vitamin B12 appear normal.

    An MMA test may be requested as a follow-up to an elevated homocysteine result if the two tests were not requested together.

    Occasionally, MMA testing may be requested when a doctor suspects that an acutely ill infant may have inherited methylmalonic acidaemia.

  • What does the test result mean?

    If MMA and homocysteine concentration are increased and B12 concentrations are mildly decreased, then an early or mild B12 deficiency may be present. This may indicate a decrease in available B12 at the tissue level. (If only homocysteine levels are elevated, then folate concentrations should be checked). If MMA and homocysteine levels are normal, vitamin B12 deficiency is unlikely.

    Since MMA is requested to detect elevated levels in suspected cases of vitamin B12 deficiency or to investigate for methylmalonic academia, decreased levels of MMA are not clinically significant.

    Blood MMA concentration can also be increased with kidney disease, which results in decreased MMA excretion in the urine and accumulation in the blood. Other conditions, which cause elevated MMA levels in the blood, are small bowel bacterial overgrowth or dehydration.


  • Is there anything else I should know?

    An elevated MMA test may indicate a vitamin B12 deficiency, but the amount of MMA measured does not necessarily reflect the severity of the deficiency, its likelihood of progressing, or the presence or severity of any symptoms. Some studies have found a high variation in MMA levels when they are measured over time.

  • If I have an elevated MMA, why might my doctor hesitate to diagnose me with vitamin B12 deficiency?

    If your vitamin B12 test result is at the low end of the normal range and you do not have significant symptoms, your doctor may feel that you have adequate vitamin B12 and will rely on these findings rather than the elevated MMA. This may be especially true if your homocysteine level is normal. Your doctor may want to monitor your condition over time and response to dietary, or other medication, changes.

  • Can either blood or urine be used for the MMA test?

    In most cases, blood is more frequently used in adults being investigated for suspected vitamin B12 deficiency. Random urine is routinely requested in children investigated for inherited metabolic disorders, including methylmalonic acidaemia.