You may think of it as just a vitamin you pass in the drugstore aisle, but B12 plays a supporting role in some of the body's most essential functions, from making red blood cells and DNA to supporting your nervous system.
This test measures the level of B12 (also called cobalamin) found in your blood. Lower than normal levels of B12 may cause fatigue, muscle weakness, intestinal problems, numbness, memory loss, anemia, as well as irreversible nerve damage if left untreated. Higher than normal levels of B12 may indicate a health condition, such as liver disease or diabetes.
No special preparation.