The stage at which neurologic damage occurs is not known but may predate macrocytosis and anemia. Persons who are vegans, who are infected with HIV, who are receiving prolonged antacid therapy, or who have had stomach or small-bowel surgery or disease should be monitored for early deficiency. The serum vitamin B 12 determination remains the most practical way to discover vitamin B 12 depletion. The Schilling test is not as useful in the elderly because decreased vitamin B 12 absorption is usually not due to lack of intrinsic factor, and treatment of all vitamin B 12 deficiency is similar. Oral and nasal replacement forms of vitamin B 12 are available, but elderly persons with symptoms or signs of deficiency should be given monthly IM injections of vitamin B 12 .
Folic acid plays a major role in lowering homocysteine levels.
The role of folic acid in preventing or treating these diseases is being studied. Macrocytosis and anemia may develop with prolonged deficiency. Folic acid deficiency may also play a role in depression but does not cause a slowly progressive dementia. Measurement of serum folic acid levels is a reasonable test for deficiency unless the patient's diet has changed recently, in which case red blood cell folic acid levels should be measured. It also helps to reactivate vitamin E, another antioxidant.