MMA is a substance produced in very small amounts in the body. It is necessary for metabolism and energy production. In one step of metabolism, vitamin B12 promotes the conversion of methylmalonyl CoA (a form of MMA) to succinyl Coenzyme A. If there is not enough B12 available, then the MMA level begins to rise, resulting in an increase of MMA in the blood and urine. Measuring methylmalonic acid in the blood or urine can help detect early vitamin B12 deficiency.
There are currently no guidelines for screening asymptomatic adults for vitamin B12 deficiency, but confirmation with MMA and/or homocysteine may be necessary for those at high risk without symptoms, such as the elderly, or when certain medications have been taken for a long time.
MMA is a very sensitive test in indicating a B12 deficiency. It is more specific than homocysteine and is the confirmatory test of choice for a B12 deficiency.
Occasionally, specialized MMA testing may be ordered to help diagnose methylmalonic acidemia, a rare inherited metabolic disorder. Newborn screening programs in all 50 states in the U.S. now require testing for this disorder (see Newborn Screening).
Tingling, numbness, and/or burning in the feet, hands, arms, and legs (with B12 deficiency)
Confusion or forgetfulness
MMA is also ordered for asymptomatic adults who have a higher likelihood of having vitamin B12 deficiency, such as the elderly, or for those taking certain drugs, like Metformin, for a long time. An MMA test also may be ordered as a follow-up to an elevated homocysteine level if the two tests are not ordered together.
MMA testing may be ordered when a health practitioner suspects that an acutely ill infant may have inherited methylmalonic acidemia.
If only the homocysteine level is elevated and not MMA, then the person may have a folate deficiency. This distinction is important because giving folate to some who is B12-deficient will treat the anemia but does not treat the neurologic damage, which may be irreversible.
If both MMA and homocysteine levels are normal, then it is unlikely that there is a B12 deficiency.
Moderately to severely elevated levels of MMA may be seen in infants with the rare inherited disease methylmalonic acidemia.
A decreased level of MMA is not common and is not considered clinically significant.
An elevated MMA test may indicate a 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.
If an individual has kidney disease, he may have a falsely high level of MMA in his blood. If the kidneys are not functioning properly, they cannot properly eliminate MMA in the urine, causing MMA to accumulate in the blood.
Some studies have found a high variation in MMA levels when they are measured over time.
This article was last reviewed on September 25, 2015. | This article was last modified on September 25, 2015.
The review date indicates when the article was last reviewed from beginning to end to ensure that it reflects the most current science. A review may not require any modifications to the article, so the two dates may not always agree.
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