Some researchers have suggested using MMA as a screening tool, especially among the elderly, who frequently have B12 deficiencies and may have few recognizable symptoms. However, this use is still controversial in the medical community and only a few doctors are using MMA for this purpose. MMA testing may not be suitable for monitoring because it is subject to variation and results do not reliably trend up or down in response to B12 treatment. Though it is a very sensitive test in indicating a B12 deficiency, it is not specific enough to provide a firm diagnosis.
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).
Methylmalonic acid is not ordered frequently. Until there are more data supporting a consensus of its clinical usefulness and long-term benefits, it will probably not be routinely ordered by doctors.
However, MMA may be ordered, sometimes along with a homocysteine test, when a vitamin B12 test result is in the lower portion of the normal range, especially if a person has symptoms associated with B12 deficiency. 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 doctor suspects that an acutely ill infant may have inherited methylmalonic acidemia.
If MMA and homocysteine levels are increased and the vitamin B12 level is 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 the homocysteine level is elevated, then the person may have a folate deficiency. 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 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 January 10, 2012. | This article was last modified on February 10, 2012.
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