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. Sometimes the amount of folate inside red blood cells may also be measured.
Folate refers to a natural occurring form of the vitamin, whereas folic acid refers to the supplement added to foods and drinks. It is found in leafy green vegetables, citrus fruits, dry beans and peas, liver, and yeast. 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 (identified as "folic acid" on nutritional labels).
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.
Folate is necessary for cell division such as is seen in a developing fetus. Folate deficiency during early pregnancy can increase the risk of neural tube defects such as spina bifida in a growing fetus.
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:
Dietary deficiencies?these are uncommon in the United States because many foods and drinks are supplemented with these vitamins, which are stored by the body. Adults typically have several years' worth of vitamin B12 stored in the liver and about 3 months of stored folate. Dietary deficiencies do not usually cause symptoms until stores of the vitamins within the body have been depleted. B12 deficiencies are sometimes seen in vegans (those who do not consume any animal products) and in their breast-fed infants.
Inadequate absorption?vitamin B12 absorption occurs in a series of steps. B12 is normally released from food by stomach acid and then, in the small intestine, is bound to intrinsic factor (IF), a protein made by parietal cells in the stomach. This B12-IF complex is then absorbed by the small intestine, bound by carrier proteins (transcobalamins), and enters the circulation. If a disease or condition interferes with any of these steps, then B12 absorption is impaired.
Increased need?this can be seen with a variety of diseases and conditions. Increased demand for folate occurs when a woman is pregnant or nursing, in early childhood, with cancers, or with chronic hemolytic anemias.
To help diagnose one cause of anemia or neuropathy; to evaluate nutritional status in some people; to monitor the effectiveness of treatment for vitamin B12 or folate deficiency. When you have an abnormal complete blood count (CBC) with a blood smear showing large red blood cells (macrocytosis) or abnormal (hypersegmented) neutrophils; when you have symptoms of anemia (weakness, tiredness, pale skin) and/or of neuropathy (tingling or itching sensations, eye twitching, memory loss, altered mental status); when you are being treated for vitamin B12 or folate deficiency.
B12 levels may be ordered when a complete blood count (CBC) and/or blood smear, done as part of a health checkup or an evaluation for anemia, indicates a low red blood cell (RBC) count with the presence of large RBCs. Specifically, a high mean corpuscular volume (MCV) indicates that the RBCs are enlarged.
Testing for B12 and folate levels may be appropriate when a person has signs and symptoms of a deficiency, such as:
Fatigue, muscle weakness
Loss of appetite
Rapid heart rate, irregular heartbeats
Shortness of breath
Sore tongue and mouth
Tingling, numbness, and/or burning in the feet, hands, arms, and legs (with B12 deficiency)
Confusion or forgetfulness
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.