Methylmalonic acid (MMA) is a dicarboxylic acid that is a C-methylated derivative of malonate. The coenzyme A linked form of methylmalonic acid, methylmalonyl-CoA, is converted into succinyl-CoA by methylmalonyl-CoA mutase, in a reaction that requires vitamin B12 as a cofactor. In this way, it enters the Krebs cycle, and is thus part of one of the anaplerotic reactions. Increased methylmalonic acid levels may indicate a vitamin B12 deficiency. However, it is sensitive but not specific. MMA is elevated in 90-98% of patients with B12 deficiency.MMA test is not routinely recommended in the elderly. An excess is associated with methylmalonic acidemia. MMA concentrations in blood are measured by Gas chromatographic Mass spectrometry and the expected values of MMA in healthy people are between 73-271 nmol/L.
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