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Why is the MMA Test Ordered?
The MMA blood test is usually ordered when a person has signs of vitamin B12 deficiency. It usually helps to confirm the diagnosis, especially when a vitamin B12 test reveals a low concentration of vitamin B12 in the blood. The symptoms that prompt a doctor to order an MMA blood test usually include numbness and tingling in the hands and feet.
The MMA blood test is also used to screen newborn babies for a rare metabolic disorder called methylmalonic acidemia. This disorder is characterized by the inability to process methylmalonyl CoA. As a result, certain symptoms arise including seizures, metal retardation, stroke, and metabolic acidosis.
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What Does the Test Measure?
The MMA blood test measures the level of methylmalonic acid in the blood. In a healthy individual, methylmalonic acid is normally produced in low quantities as a byproduct of amino acid metabolism. Any increase in the concentration of methylmalonic acid in the blood usually indicates a problem with vitamin B12.
Vitamin B12 is required to convert methylmalonic CoA to succinyl CoA in the normal metabolic process. If there is not enough vitamin B12 to convert methylmalonic CoA to succinyl CoA, then the amount of methylmalonic CoA increases. As a result, methylmalonic CoA is converted to an alternative form, namely methylmalonic acid.
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How is the Test Performed?
The MMA blood test requires a blood sample that is drawn from a vein in the arm. Before giving the blood sample, one may need to fast for a period of time. Consult with the doctor to determine an adequate length of time to avoid food before taking the test.
Along with the MMA blood test, a homocysteine blood test may be ordered as well. The additional test helps to confirm vitamin B12 deficiency. The homocysteine blood test also requires fasting before the sample is taken.
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Test Results for MMA
The results of the MMA blood test show how much methylmalonic acid is in the blood. If the level of methylmalonic acid in the blood is elevated, the homocysteine level is high, and the vitamin B12 level is low, then the cause is vitamin B12 deficiency. The severity of the deficiency is usually described as early or mild.
An increased level of methylmalonic acid may also indicate kidney disease. Other tests are needed to confirm kidney disease, but the elevated level of methylmalonic acid in the blood may be due to the decreased excretion of methylmalonic acid in the urine.
If the test is done on infants, and the level of methylmalonic acid is extremely high, the cause is most likely methylmalonic acidemia. The severity of the disease can range from mild to life threatening.