An MMA test is most often used to diagnose a vitamin B12 deficiency. The test is usually also included as part of a series of tests called a newborn screening. A newborn screening checks for a variety of health conditions. An MMA test checks for methylmalonic acidemia, a rare genetic disorder.

Methylmalonic acid (MMA) is a substance that is created when your body digests protein. The amount of vitamin B12 in your body controls how much MMA your body makes. A high amount of MMA typically means you have a vitamin B12 deficiency. There are two types of low-risk methylmalonic acid tests.