Vitamin B12 and folate are two vitamins that are part of the B complex of vitamins. They are necessary for normal red blood cell (RBC) formation, repair of tissues and cells, and synthesis of DNA, the genetic material in cells. Both are nutrients that cannot be produced in the body and must be supplied by the diet. Vitamin B12 and folate tests measure vitamin levels in the liquid portion of the blood (serum or plasma) to detect deficiencies. Vitamin B12, also called cobalamin, is found in foods from animals, such as red meat, fish, poultry, milk, yogurt, and eggs. In recent years, fortified cereals, breads, and other grain products have also become important dietary sources of B12 and folate A deficiency in either B12 or folate can lead to macrocytic anemia, where red blood cells are larger than normal. Megaloblastic anemia, a type of macrocytic anemia, is characterized by the production of fewer but larger RBCs called macrocytes, in addition to some cellular changes in the bone marrow. Other laboratory findings associated with megaloblastic anemia include decreased white blood cell (WBC) count and platelet count. B12 is also important for nerve health and a deficiency can lead to varying degrees of neuropathy, nerve damage that can cause tingling and numbness in the affected person's hands and feet
B12 and folate deficiencies are most often caused by not getting enough of the vitamins through the diet or supplements, inadequate absorption, or by increased need as seen in pregnancy: B12 and folate testing may sometimes be ordered when a person is at risk of a deficiency, such as people with a history of malnutrition or a condition related to malabsorption. These tests may be ordered on a regular basis for individuals being treated for malnutrition or a B12 or folate deficiency to evaluate the effectiveness of their treatments. For individuals with a condition causing a chronic deficiency, this may be part of a long-term treatment plan. If a person is deficient in both B12 and folate but only takes folic acid supplements, the B12 deficiency may be masked. The anemia associated with both may be resolved, but the underlying neuropathy will persist. Intrinsic factor antibodies can interfere with the vitamin B12 test, producing falsely elevated results. If a person has these antibodies in their blood, the results of their B12 test must be interpreted with caution.