Use

Serum methylmalonic acid (MMA) measurement is used to evaluate individuals with signs and symptoms associated with vitamin B₁₂ deficiency or congenital methylmalonic academia.

MMA is a product of the metabolic break-down of valine, isoleucine, and propionic acid. Vitamin B12 is a critical cofactor for the conversion of MMA to succinate. As a result, vitamin B₁₂ deficiency causes an accumulation of MMA in the serum. MMA concentrations will often become elevated in the early stages of vitamin B₁₂ deficiency while serum vitamin B₁₂ levels are in normal range. Consequently, MMA measurement is used as a diagnostic test for vitamin B₁₂ deficiency in persons with a low or low normal serum vitamin B₁₂ concentration. Follow-up measurement of MMA can also be of value in assessing the effectiveness of vitamin B₁₂ supplementation of deficient patients.

Vitamin B₁₂ deficiency causes macrocytic anemias and decreased erythrocyte (red blood cell) survival due to abnormal maturation of erythrocyte precursors in the bone marrow. Pernicious anemia is a form of vitamin B₁₂ deficiency that is caused by a lack of intrinsic factor. Low vitamin B₁₂ intake, gastrectomy, malabsorption, and transcobalamin deficiency can also cause vitamin B₁₂ deficiency. Although severe vitamin B₁₂ deficiency is associated with anemia, hematologic signs are not always observed in patients with biochemically confirmed deficiency. Elderly patients with cobalamin deficiency may present with peripheral neuropathy, ataxia, memory impairment, depression, and dementia in the absence of anemia.

A generally agreed on cutoff for elevated plasma MMA is 370 nmol/L. Approximately 2% of the US population and 7% of elderly persons have MMA concentrations above this threshold.