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- Vitamin B12 and Folate
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 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.
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:
For more, see the article on Vitamin B12 and Folate Deficiencies.
Vitamin B12 and folate are separate tests often used together to:
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.
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.
Testing for B12 and folate levels may be ordered when you have signs and symptoms of a deficiency, such as:
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.
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:
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.
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).
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.
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
These tests are generally not necessary if you do not have symptoms associated with a deficiency, you do not have large red blood cells (RBCs) as determined by a complete blood count (CBC), or you do not have a disease or condition associated with malabsorption.
Folate levels may be tested during prenatal checkups. Folate supplementation is generally recommended for women before and during pregnancy.
These tests require specialized equipment and are typically performed in a laboratory.
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