Vitamin B12 and Folate
Also known as:
Cobalamin; Folic Acid; RBC Folate
Vitamin B12; Folate
Vitamin B12 and folate are primarily ordered to detect deficiencies and to help diagnose the cause of certain
anemias. One type of associated anemia is pernicious anemia, an autoimmune disease that affects the
absorption of B12. This megaloblastic anemia occurs when the body produces antibodies against the gastric parietal cells or the intrinsic factor, resulting in B12 malabsorption.
Folate, B12, and an assortment of other tests may be ordered to help evaluate the general health and
nutritional status of a person with signs of significant malnutrition or dietary malabsorption. This may
include people with alcoholism, other liver diseases, gastric cancer, and those with malabsorption conditions
such as celiac disease, tropical sprue, Crohn disease,inflammatory bowel disease, and cystic fibrosis.
B12 and folate may also be ordered to aid in diagnosis when an individual presents with an altered mental
state or other behavioral changes, especially in the elderly. B12 may be ordered with folate, by itself, or
with other screening laboratory tests (antinuclear antibody, CRP, rheumatoid factor, CBC and chemistry
blood tests) to help establish reasons why a person shows symptoms of neuropathy.
In those treated for known B12 and folate deficiencies, these tests will be ordered occasionally to monitor
the effectiveness of treatment. This is especially true in those who cannot properly absorb B12 and/or folate and must have lifelong treatment. Serum folate levels can vary based on dietary intake. RBCs can store 95% of circulating folate, thus a RBC
folate level may be used to help detect a deficiency. Some doctors feel that the RBC folate test 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 CBC, done routinely or as part of an evaluation for anemia,
indicates the presence of large RBCs. This increased RBC size is reflected in the RBC indices, specifically the
Testing for B12 and folate levels may be appropriate when a person, especially an elderly person, exhibits a
sudden or unexplained mental or behavioral change, such as irritability, confusion, depression, and/or
paranoia. Testing may also be ordered when someone has physical symptoms that suggest a B12 or folate
deficiency, including dizziness, weakness, fatigue, or a sore mouth or tongue.
When a person has symptoms suggesting nerve damage or impairment (neuropathy), such as, tingling, burning, or numbness in their hands, arms, legs, and or/feet, a B12 test may be requested to help
determine the cause. B12 and folate testing may sometimes be ordered as part of a general health evaluation when a person
shows signs of or has a history of malnutrition or malabsorption. When a breastfed infant has a B12 or folate
deficiency, then the mother may also be tested to see if she has a deficiency that is affecting both her and
What does the test result mean?
Serum B12 and folate tests are snapshots of the concentrations in the blood. Normal values may indicate
that a person's symptoms are likely due to another cause or they may reflect the fact that a person's stores
of B12 and/or folate have not yet been fully exhausted. When a B12 is normal but a deficiency is still suspected, a doctor may order a methylmalonic acid (MMA) test as an early indicator of B12 deficiency.
In a symptomatic person, decreased concentrations of B12 and/or folate indicate the presence of a
deficiency, but do not necessarily reflect the severity of the anemia or associated neuropathy. Further
investigation of the underlying cause of the deficiency is then pursued. Some causes of low B12 or folate
· Insufficient intake—Dietary deficiency of folate or B12 is uncommon in the U.S. It sometimes may be seen
with genera lmalnutrition and in vegans who do not consume any animal products, including milk and eggs. With the introduction of fortified cereals, breads, and other grain products, folate deficiency is very rare.
· Malabsorption—Both B12 and folate deficiencies may be seen with conditions that interfere with their
absorption in the small intestine. These may include:
o Bacterial overgrowth or the presence of parasites in the intestines o Reduced stomach acid production from long-term use of antacids or H2 proton pump inhibitors
o Pernicious anemia, the most common cause of B12 deficiency
o Surgery that removes part of the stomach, such as gastric bypass, or the intestines may greatly decrease
· Chronic alcoholism can cause B12 and/or folate deficiency due to poor intake and impaired release of B12
· Some drugs can cause B12 deficiency, such as metformin and omeprazole, which cause B12 malabsorption and impaired release of B12 from food proteins due to decrease in gastric acids, respectively.
· Anti-seizure medications such as phenytoin can decrease folate as can drugs such as methotrexate, which
blocks folate absorption and affect body metabolism and utilization of folate, respectively.
· Increased need--All pregnant women need increased amounts of folate for proper fetal development.
People with cancer that has spread (metastasized) or with chronic hemolytic anemia have increased need for folate.
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.
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