Methylmalonic Acid

This is a test used to help detect early and/or mild vitamin B12 deficiency, especially at the tissue level. It is also used to help diagnose methylmalonic acidemia, a rare inherited metabolic disorder. The test may be done if you have a vitamin B12 concentration in the low end of the normal range and/or have symptoms of neuropathy, such as numbness and tingling in the hands and feet.

The methylmalonic acid (MMA) test is a sensitive and early indicator of vitamin B12 deficiency at the tissue level. MMA is a compound that is usually produced in very small amounts during amino acid (protein) metabolism. Normally, B12 acts as a cofactor in the conversion of methylmalonyl CoA to succinyl CoA. If there is not enough B12 to act as a cofactor, then methylmalonyl CoA concentrations begin to rise and the body converts the methylmalonyl CoA to MMA instead. This causes MMA levels to rise in both the blood and the urine when B12 levels are low.

SAMPLE COLLECTION

This test may be performed on blood or urine. Your caregiver will instruct you on what is required.

NORMAL FINDINGS

Normal findings depend on many factors. Your lab will provide a range of normal findings with your test results.

Ranges for normal findings may vary among different laboratories and hospitals. You should always check with your doctor after having lab work or other tests done to discuss the meaning of your test results and whether your values are considered within normal limits.

MEANING OF TEST

A standard reference range is not available for this test. Because reference values are dependent on many factors, including patient age, gender, sample population, and test method, numeric test results have different meanings in different labs. Your lab report should include the specific reference range for your test.

If MMA and homocysteine levels 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, it is unlikely that there is a B12 deficiency.

Blood MMA levels also can be increased with kidney disease, which results in decreased MMA excretion in the urine so MMA accumulates in the blood.

Moderately to severely elevated levels of MMA may be seen in infants with the rare inherited disease methylmalonic acidemia.

OBTAINING THE TEST RESULTS

It is your responsibility to obtain your test results. Ask the lab or department performing the test when and how you will get your results.