The Test Sample
What is being tested?
These tests measure the concentration of folate and vitamin B12 in the serum (liquid portion of the blood).
Vitamin B12 and folate are both part of the B complex of vitamins. Folate is found in leafy green vegetables, citrus fruits, dry beans and peas, liver, and yeast. Vitamin B12 is found in animal products such as red meat, fish, poultry, milk, and eggs. In recent years fortified cereals, breads, and other grain productshas also become an important dietary sources of folate (identified as "folic acid" on nutritional labels).
Both vitamin B12 and folate are necessary for normal red cell formation, tissue and cellular repair, and DNA synthesis. Vitamin B12 is also important for nerve health, while folate is necessary for cell division such as is seen in a foetus during pregnancy. A deficiency in either vitamin B12 or folate can lead to macrocytic anaemia, where red cells are reduced but macrocytic (abnormally large). Specifically a bone marrow test may show megaloblastic anaemia, where immature red cells called megaloblasts may be seen. It is usually unnecessary for a bone marrow test to be performed for diagnosis of vitamin B12 deficiency.
Vitamin B12 deficiency can also result in varying degrees of neuropathy, nerve damage that can cause tingling and numbness in the patient's hands and feet. In severe vitamin B12 deficiency, a more serious nerve damage may occur known as subacute combined degeneration of the cord or SACD, where severe weakness and incoordination may occur. Subtle deterioration in eyesight and mental ability may occur. Folate deficiency in early pregnancy can cause neural tube defects such as spina bifida in a growing foetus.
There are a variety of causes of vitamin B12 and/or folate deficiencies. They include:
The human body stores several years’ worth of vitamin B12 in the liver. Vitamin B12 is widely available in non-vegan foods, so a dietary deficiency of this vitamin is rare. It may be seen sometimes with general malnutrition, and in vegan vegetarians - those who do not consume any animal products including milk and eggs. It may also be seen in children and breastfed infants of vegan vegetarians. Since they do not have the stores that adults do, deficiencies in children and infants show up fairly quickly. Vitamin B12 deficiency is extremely uncommon in children but can be rarely seen with genetic defects involving vitamin B12 metabolism.
Folate deficiency used to be common but with the advent of fortified cereals, breads, and grain products it is less so. Since folate is stored in tissue in smaller quantities than vitamin B12, folate must be consumed more regularly than vitamin B12.
Both vitamin B12 and folate deficiencies may be seen with conditions that interfere with their absorption in the small intestine. These may include:
- Coeliac disease (specifically folate deficiency)
- Bacterial overgrowth in the stomach and intestines
- Reduced stomach acid production (stomach acid is necessary to separate B12 from the protein in food)
- Pernicious anaemia , the most common cause of vitamin B12 deficiency. Normally a molecule called intrinsic factor is made by parietal cells that line the stomach. B12 binds to intrinsic factor in the stomach, and the resulting complex is absorbed in the small intestines (ileum). With pernicious anaemia, antibodies attack parietal cells, reducing intrinsic factor production, or attack intrinsic factor, blocking its action, in either case preventing the efficient absorption of B12.
- Surgery that removes part of the stomach (and the parietal cells) or the intestines may greatly decrease absorption
- Crohns disease affecting the end of the small intestine (ileum)
- the type 2 diabetes drug Metformin may affect B12 levels
- Alcoholism, with alcohol abuse less B12 and folate are absorbed and more are excreted from the kidneys
All pregnant women need increased amounts of folate for proper fetal development. If a woman has a folate deficiency prior to pregnancy, it will be intensified during gestation, and may lead to premature birth and neural tube defects in the child.
How is the sample collected for testing?
A blood sample is obtained by inserting a needle into a vein in the arm.
NOTE: If undergoing medical tests makes you or someone you care for anxious, embarrassed, or even difficult to manage, you might consider reading one or more of the following articles: Coping with Test Pain, Discomfort, and Anxiety, Tips on Blood Testing, Tips to Help Children through Their Medical Tests, and Tips to Help the Elderly through Their Medical Tests.
Another article, Follow That Sample, provides a glimpse at the collection and processing of a blood sample and throat culture.
Is any test preparation needed to ensure the quality of the sample?
No special preparation for a standard vitamin B12 blood test.