This blood test is used to measure vitamin B12 and Folic Acid levels. Folic acid deficiency is common in pregnant women, alcoholics, patients with diets that do not include raw fruits and vegetables, and people with structural damage to the small intestine. The most reliable and direct method of diagnosing folate deficiency is the determination of folate levels in both erythrocytes and serum. Low folic acid levels, however, can also be the result of a primary Vitamin B12 deficiency that decreases the ability of cells to take up folic acid. B12 is decreased in pernicious anemia, total or partial gastrectomy, malabsorption and certain congenital biochemical disorders.