Also known as: Vitamin B12 or cobalamin; folic acid, RBC folate
Name: Vitamin B12 and folate (or folic acid)
Related tests: Full blood count, CMP
Why get tested?
To help diagnose anaemia or neuropathy (nerve damage), to assess the nutritional status of some patients, and to monitor the effectiveness of treatment for vitamin B12 or folate deficiency.
When to get tested?
When you have large red blood cells, or symptoms of anaemia and/or neuropathy. When you are being treated for vitamin B12 or folate deficiency.
Sample required?
A blood sample taken from a vein in the arm
What is being tested?
These tests measure the concentration of folate and vitamin B12 in the serum (the liquid part of the blood). The amount of folate inside red blood cells (RBCs) can also be measured; it is normally at a higher concentration in the cells than in the serum. B12 and folate are both part of the vitamin B complex and are taken in with the diet. Folate is found in green leafy vegetables, citrus fruits, dried beans and peas, liver and yeast, while B12 is found in animal products such as red meat, fish, poultry, milk and eggs. Cereals, bread and other wheat products are also dietary sources of B12 and folate (shown as “folic acid” on nutrition labels), especially for vegetarians who do not eat animal products.
Both B12 and folate are needed for normal red blood cell formation, tissue and cell repair and DNA synthesis. B12 is also important for the health of the nervous system, while folate is needed for cell division, as in the foetus during pregnancy. A deficiency of either B12 or folate can lead to a form of anaemia characterised by the production of few but large red blood cells (called macrocytes). B12 deficiency can also lead to varying degrees of neuropathy, nerve damage that can cause tingling and numbness in the hands and feet. Folate deficiency can cause neural tube defects such as spina bifida in the foetus
How is it used?
When is it requested?
What does the test result mean?
Is there anything else I should know?
How is it used?
B12 and folate are mainly requested to diagnose the cause of macrocytic anaemia. They are requested as follow-up tests when large red blood cells and a low haemoglobin concentration are found. Folate, B12 and a range of other tests may be requested to assess the general and nutritional status of patients with signs of significant malnutrition or malabsorption. These may include patients with alcoholism and those with disorders associated with malabsorption, such as coeliac disease, Crohn’s disease and cystic fibrosis. B12 and folate also help diagnose the causes of mental or behavioural changes, especially in elderly people. B12 may be requested with folate, on its own or with other laboratory tests, such as the CMP (comprehensive metabolic panel), to diagnose neuropathy.
In patients with known folate and B12 deficiencies, these tests may be requested occasionally to monitor the effectiveness of treatment. This is especially true in patients who cannot absorb B12 and/or folate and need long-term treatment.
Serum folate or RBC folate should help detect a deficiency. Some doctors consider RBC folate more clinically relevant than serum folate, but there is no unanimous agreement on this.
When is it requested?
B12 and folate are mainly measured when a full blood count, done routinely or to assess symptoms of anaemia, shows large red blood cells.
When a person, especially an elderly person, shows behavioural changes such as irritability, confusion, depression and/or paranoia, B12 and folate can help determine the cause. They may also be requested when there are physical symptoms suggesting B12 or folate deficiency, such as exhaustion, weakness, tiredness and a sore throat.
When a patient has symptoms of nerve damage such as tingling, burning or numbness in the hands, arms, legs and/or feet, a B12 test should be requested to diagnose the cause and detect B12 deficiency. B12 may be requested on its own, together with folate, and/or together with other tests such as the CMP.
B12 and folate may sometimes be requested as part of a general health assessment when the patient shows signs of malnutrition or malabsorption or is known to have a disorder that affects food absorption. If a breastfed baby has B12 or folate deficiency, the mother should also be tested to see whether she has a deficiency affecting both her and the baby.
When a patient is being treated for B12 or folate deficiency, they are usually monitored occasionally to assess the effectiveness of treatment. In a person with nutritional deficiencies, this may be done as follow-up. In chronic deficiency, this test is part of a long-term treatment plan.
What does the test result mean?
The doctor is looking for B12 and/or folate deficiency. If a patient with symptoms has a low B12 and/or folate concentration, they probably have some form of deficiency. The test result shows that a deficiency is present but does not necessarily reflect the severity of the associated anaemia or neuropathy, or its cause.
There are several causes of B12 and/or folate deficiency. They include:
Insufficient intake
The human body stores enough B12 in the liver to last several years, and it is readily available in food, so a dietary deficiency of this vitamin is extremely rare in the USA. It may sometimes be found in general malnutrition and in strict vegetarians (vegans), who do not eat any animal products, including milk and eggs. It may be found in the children of vegans and in breastfed babies. Since they do not have the stores that adults have, deficiencies in children and babies appear quickly.
Folate deficiency used to be common, but with the introduction of fortified cereals, bread and wheat products it is now less frequent. Since folate is stored in the tissues in smaller amounts than B12, folate must be consumed more regularly than B12.
Malabsorption
Both folate and B12 deficiencies are found in conditions that interfere with their absorption from the gut. These include:
• Coeliac disease (gluten intolerance that causes inflammation and malabsorption)
• Bacterial overgrowth in the stomach and intestine
• Reduced production of stomach acid (stomach acid is needed to separate B12 from the proteins in food)
• Pernicious anaemia, the most common cause of B12 deficiency. Normally a molecule called intrinsic factor is produced by the parietal cells of the stomach. B12 binds to intrinsic factor in the stomach, and the resulting molecule is absorbed in the intestine. In pernicious anaemia, little or no intrinsic factor is produced, preventing the absorption of B12.
• Surgery that removes part of the stomach (and the parietal cells) or the intestine can greatly reduce absorption
Increased loss.
This can be found in:
• Liver and kidney disease
• Alcoholism: with alcohol abuse, less B12 and folate are absorbed and more are excreted through the kidneys
• Medicines such as phenytoin (Dilantin) can lower folate, as can some drugs such as metformin and methotrexate
Increased need
Pregnant women need more folate for the baby to develop properly. If a woman already has a folate deficiency before pregnancy, it will get worse during pregnancy and can lead to premature birth and neural tube defects in the baby.
If a patient with B12 or folate deficiency is treated with supplements (or B12 injections), normal or high values indicate a response to treatment.
Is there anything else I should know?
If a patient is deficient in both folate and B12 but takes only folate supplements, the B12 deficiency may be masked. The anaemia associated with both may resolve, but the underlying neuropathy (nerve damage) persists.
The Schilling test used to be requested fairly often to confirm pernicious anaemia as the cause of B12 deficiency. It is still requested occasionally but is falling out of use because it requires radioactive B12 to be given. The Schilling test has partly been replaced by tests for intrinsic factor antibodies and parietal cell antibodies
1. Can taking too many vitamin B12 and folate supplements harm me?
2. Is there a difference between folate and folic acid?
1. Can taking too many vitamin B12 and folate supplements harm me?
Usually not. Since folate and B12 are water-soluble, the body will eliminate the excess in the urine.
2. Is there a difference between folate and folic acid?
No, they are the same thing