Laboratory Medicine Program

Methylmalonic Acid
(MMA)

Clinical Decription:
Methylmalonic acid is an organic acid found normally in the blood, but not in the urine. In vitamin B12 deficiency, serum MMA increases due to deficient activity of an enzyme, methylmalonyl-CoA mutase, that metabolizes MMA. There are only two B12-requiring enzymes in the body. The other enzyme is methionine synthase, which remethylates homocysteine. Thus, B12 deficiency may also cause increased plasma total homocysteine. Deficiency of vitamin B12 remains endemic in the general population but most individuals are asymptomatic. It is more common in the elderly and in those adhering to strict vegetarian diets. The appropriate screening tests for B12 deficiency are: 1) medical examination for specific signs and symptoms; 2) measurement of erythrocyte volume (RBC MCV) and hematologic review to detect megaloblastic anemia; 3) assay of serum total B12. This is usually sufficient to suggest appropriate treatment or further assessment and testing. In some cases, however, screening may not provide a definitive answer. In particular, the serum B12 assay does not have a clear cut-off point. There is a "grey zone", generally between 90 and 150 pmol/L, into which B12-deficient patients may fall. Less commonly, there are healthy individuals with very low serum B12 results and B12-deficient patients with normal serum levels. For this reason, plasma MMA has been considered a useful confirmatory test. Used in conjunction with the clinical and hematologic information, as well as a serum B12 level, and sometimes a total plasma homocysteine, it should provide the practitioner with sufficient information to decide whether therapy is warranted or not.

Method: LC-MS/MS; LC-MS

Component Tests Used: n/a

Reference Ranges Used:
0.10-0.40 umol/L

Specimen Type: Plasma
Volume: 3 mL (minimum: 3 mL)

Shipping: Frozen at -20C

Special Instructions: Separate Plasma within 6 hours

Testing Schedule(s): 2 weeks.

Turnaround Time: 10 Business days

For more information, call 416.340.5227 or 1.866.865.5227