MMA is a substance which is produced in minor amounts in the body. It is important for metabolism and production of energy. In the single step of metabolism, vitamin B12 prompts the conversion of methylmalonyl CoA (a form of MMA) to succinyl Coenzyme A. If the B12 available is not enough, then the MMA level will begin to rise which will result in an increase of MMA in the blood and urine. Measuring methylmalonic acid in the blood or urine can help one to know about early vitamin B12 deficiency. MMA is a sensitive test which helps to know about B12 deficiency. It is more particular than homocysteine and is the confirmatory test of choice for a B12 deficiency. Sometimes, specialized MMA testing may be told to know about the methylmalonic acidemia which is a rare inherited metabolic disorder. Newborn screening programs in all 50 states in the U.S. now require testing for this disorder