Vitamin B12 and Folate
When you have abnormal results on a 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
A blood sample drawn from a vein in your arm
Biotin found in certain dietary supplements may interfere with testing. Certain medicines, such as cholchicine, neomycin, para-aminosalicylic acid, and phenytoin, may affect the test results; your healthcare provider will advise you on which ones to stop taking. Ask your healthcare practitioner or lab for specific instructions.
Vitamin B12 and folate are two vitamins that are part of the B complex of vitamins. B12 and folate work with vitamin C to help the body make new proteins. They are necessary for normal red blood cell (RBC) and white blood cell (WBC) formation, repair of tissues and cells, and synthesis of DNA. 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.
- Vitamin B12, also called cobalamin, is found in foods from animals, such as red meat, fish, poultry, milk, yogurt, and eggs.
- Folate (Vitamin B9) refers to a natural occurring form of the vitamin, whereas folic acid refers to the supplement added to foods and drinks. Folate is found in leafy green vegetables, citrus fruits, dry beans and peas, liver, and yeast.
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 WBC count, RBC count, reticulocyte 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, long-term use of certain medications, 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.
For more, see the article on Vitamin B12 and Folate Deficiencies.
How is the test used?
Vitamin B12 and folate are separate tests often used together to:
- Detect low levels (deficiencies)
- Diagnose the cause of certain anemias, such as pernicious anemia, an autoimmune disease that affects the absorption of B12
- Help determine the cause of an altered mental state or other behavioral changes, especially in the elderly
- Help determine the cause of signs and symptoms of a condition affecting nerves (neuropathy)
- Evaluate your general health and nutritional status if you have signs and symptoms of significant malnutrition or dietary malabsorption.
- Monitor the effectiveness of treatment with vitamin B12 and folate supplements; this is especially true for those who cannot properly absorb B12 and/or folate and must have lifelong treatment.
Serum folate levels can vary based on a person's recent diet. Because red blood cells store 95% of circulating folate, a test to measure the folate level within RBCs may be used in addition to the serum test. Some healthcare practitioners feel that the RBC folate test is a better indicator of long-term folate status and is more clinically relevant than serum folate, but there is not widespread agreement on this.
When is it ordered?
B12 and folate 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, shows a low red blood cell (RBC) count, decreased hemoglobin and hematocrit, and the presence of large RBCs. Specifically, a high RBC mean corpuscular volume (MCV) indicates that the RBCs are enlarged. In addition to enlarged RBCs on the blood smear, the nucleus of white cell neutrophils show many segments (hypersegmented neutrophils), a classic sign frequently observed.
- Dizziness, trouble walking
- Fatigue, muscle weakness
- Loss of appetite
- Pale skin
- 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
- Paranoia, irritability
B12 and folate testing may sometimes be ordered when you have a condition that puts you at risk of a deficiency.
These tests may be ordered on a regular basis when you are treated for malnutrition or a B12 or folate deficiency. For individuals with a condition causing a chronic deficiency, this may be part of a long-term treatment plan.
What does the test result mean?
Normal B12 and folate blood levels may mean that you do not have a deficiency and that your signs and symptoms are likely due to another cause. However, normal levels may reflect the fact that your stored B12 and/or folate have not yet been fully depleted.
When a B12 level is normal or low normal but a deficiency is still suspected, a healthcare practitioner may order a methylmalonic acid (MMA) test as an early indicator of B12 deficiency.
A low B12 and/or folate level means that you have a deficiency. Additional tests are usually done to investigate the underlying cause of the deficiency. Some causes of low B12 or folate include:
- Conditions that interfere with their absorption in the small intestine. These may include:
- Pernicious anemia, the most common cause of B12 deficiency
- Celiac disease and tropical sprue
- Inflammatory bowel disease, including Crohns disease and ulcerative colitis
- Bacterial overgrowth or the presence of parasites, such as tapeworms, in the intestines
- Reduced stomach acid production from long-term (more than one year) use of antacids or H2 receptor blockers or proton pump inhibitors
- Surgery that removes part of the stomach, such as gastric bypass, or the intestines may greatly decrease absorption.
- Pancreatic insufficiency (exocrine pancreatic insufficiency) - the pancreas is not able to produce enough digestive enzymes to break down food.
- Dietary deficiency of folate or B12—this is uncommon in the U.S. However, it may be seen with general malnutrition, in the elderly and in vegans who do not consume any animal products. With the introduction of fortified cereals, breads, and other grain products, folate deficiency is very rare.
- Heavy drinking or chronic alcoholism
- Use of some drugs such as metformin, omeprazole, methotrexate or anti-seizure medications such as phenytoin
- Increased need—all pregnant women need increased amounts of folate for proper fetal development and are recommended to take 400 micrograms of folic acid per day. People with cancer that has spread (metastasized) or with chronic hemolytic anemia have increased need for folate.
For additional information, see the article Vitamin B12 and Folate Deficiencies.
If a person with a B12 or folate deficiency is being treated with supplements (or with B12 injections), then normal or elevated results indicate a response to treatment.
High levels of B12 are uncommon and not usually clinically monitored. However, if someone has a condition such as chronic myeloproliferative neoplasm, diabetes, heart failure, obesity, AIDS, or severe liver disease, then that person may have an increased vitamin B12 level. Ingesting estrogens, vitamin C or vitamin A can also cause high B12 levels.
- Conditions that interfere with their absorption in the small intestine. These may include:
What other tests might be done?
Additional laboratory tests may be used to help diagnose pernicious anemia, the most common cause of B12 deficiency. These include intrinsic factor antibody and parietal cell antibody. The presence of these autoimmune antibodies indicates that a B12 deficiency is likely due to the destruction of parietal cells in the stomach, leading to a decreased ability to absorb B12 from the diet.
Other laboratory tests that may be used to help detect B12 and folate deficiencies include homocysteine and methylmalonic acid (MMA). Homocysteine and MMA are elevated in B12 deficiency while only homocysteine, and not MMA, is elevated in folate deficiency. This distinction is important because giving folate to someone who is B12-deficient will treat the anemia but does not treat the neurologic damage, which may be irreversible.
When you have signs and symptoms of neuropathy, a B12 test may be ordered with folate, by itself, or with other screening laboratory tests, such as a complete blood count (CBC), comprehensive metabolic panel (CMP), antinuclear antibody (ANA), C-reactive protein (CRP), and rheumatoid factor (RF).
Is there anything else I should know?
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.
Since folate deficiency is rarely seen in the U.S., some laboratories no longer offer the folate test. Your sample may need to be sent to a reference laboratory.
Can taking too many vitamin B12 and folic acid supplements hurt me?
Not usually. B12 and folic acid are water-soluble, thus the body will rid itself of any excess by eliminating it in the urine. However, taking folic acid can mask low B12 levels, so it can be important to be tested for both before beginning folate supplementation. Individuals who are allergic to cobalt should not take B12, and those with the hereditary eye disease Leber's disease may experience harm to the optic nerve if they take B12
Should everyone have vitamin B12 and folate tests?
Should every pregnant woman have a folate test?
Can I have B12 and folate tests done in my doctor's office?