The MMA test is used to diagnose and monitor vitamin B12 deficiency, which can result in a range of symptoms including fatigue, weakness, and neurological problems. Elevated MMA levels can indicate a deficiency in vitamin B12, leading to impaired metabolic processes and potential complications such as anemia and neurological disorders. The test is essential for evaluating vitamin B12 status, especially in individuals with symptoms of deficiency or those at risk due to dietary or absorption issues.