Interpreting combinations of methylmalonic acid and homocysteine level results

This article was first published on December 15, 2023. It was last reviewed, updated, or edited on December 15, 2023. Mental health clinicians often check serum vitamin B12 levels, especially in patients with cognitive impairment or nutritional deficiency, and in patients who are vegetarian or vegan. The test that laboratories use to measure vitamin B12…