VitB12 deficiency

In neurologic symptoms caused by vitamin B12 deficiency, both homocysteine and methylmalonic acid levels are increased. Measurement of these metabolites has been shown to be more sensitive in diagnosing vitamin B12 deficiency than measuring serum B12 levels alone . Elevated methylmalonic acid levels indicate a deficiency in vitamin B12, as methylmalonic acid reacts with vitamin B12 to produce coenzyme A, which is essential for normal cellular function . Homocysteine levels also increase due to vitamin B12 deficiency, as vitamin B12 is necessary for the metabolism of homocysteine . These metabolites can serve as early markers for tissue vitamin B12 deficiency, even before hematologic manifestations occur .