At a Glance
Why Get Tested?
To help diagnose the cause of anaemia or neuropathy (nerve damage), to evaluate nutritional status in some patients, to monitor effectiveness of treatment for B12 or folate deficiency
When to Get Tested?
When you have large red blood cells, when you have symptoms of anaemia and/or of neuropathy. When you are being treated for B12 or folate deficiency
Sample Required?
A blood sample drawn from a vein in your arm
Test Preparation Needed?
Fasting for 6-8 hours before sample collection is required especially for serum folate testing
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). The amount of folate inside the red blood cell (RBC) may also be measured - it will normally be at a higher concentration inside the cell than in the serum and reflect folate level over a longer period. Vitamin B12 and folate are both part of the B complex group of vitamins and come from food. Folate is found in leafy green vegetables, citrus fruits, dry beans and peas, liver and yeast while vitamin B12 is found in animal products such as red meat, fish, poultry, milk and eggs. Fortified cereals, breads and other grain products are now also important dietary sources of folate (identified as 'folic acid' on nutritional labels), especially for those vegetarians who do not consume any animal products. Since September 2009, mandatory folate fortification of flour in Australia has significantly reduced the incidence of folate deficiency and increased blood folate levels.
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 occurs in a rapidly growing fetus during pregnancy. A deficiency in either vitamin B12 or folate can lead to a form of anaemia characterised by the production of fewer, but larger, red cells (macrocytic anaemia).
A deficiency in vitamin B12 can also result in varying degrees of neuropathy, nerve damage that can cause tingling and numbness in the patient's hands and feet. A deficiency in folate can cause neural tube defects such as spina bifida in a growing fetus.
How is the sample collected for testing?
A blood sample is obtained by inserting a needle into a vein in the arm.
Is any test preparation needed to ensure the quality of the sample?
Fasting for 6-8 hours before sample collection may be required.
Fasting is essential for serum folate as food prior to testing can influence the measured serum level.
The Test
How is it used?
Vitamin B12 and folate can be ordered to help diagnose the cause of macrocytic anaemia. They can be requested as follow-up tests when large red cells and a decreased haemoglobin concentration are found during a FBC test. Folate and vitamin B12 may be used to help evaluate the nutritional status of a patient with signs of significant malnutrition or malabsorption. This may include those with alcoholism and those with disorders associated with malabsorption such as coeliac disease, Crohn's disease and cystic fibrosis. Vitamin B12 and folate may also be ordered to help diagnose the cause of mental or behavioural changes, especially in the elderly.
In patients with known vitamin B12 and folate deficiencies, these tests may be used occasionally to help monitor the effectiveness of treatment. This is especially true in patients who cannot absorb vitamin B12 and/or folate and must have lifelong treatment. Either a serum or RBC folate test 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 requested?
Vitamin B12 and folate are usually measured when a FBC, done routinely or as part of an evaluation of anaemia, indicates the presence of large red cells.
When a person, especially an elderly person, exhibits mental or behavioural changes such as irritability, confusion, depression and/or paranoia, vitamin B12 and folate may be done to help diagnose the underlying cause. They may also be used when a patient has physical symptoms that suggest a B12 or folate deficiency, including dizziness, weakness, fatigue, or a sore mouth or tongue.
When a patient has symptoms suggesting nerve damage or impairment, such as, tingling, burning, or numbness in their hands, arms, legs, and or/feet, a vitamin B12 test may be requested to help diagnose the cause and detect the presence of a vitamin B12 deficiency. The vitamin B12 measurement may be ordered by itself or along with a folate level.
Vitamin B12 and folate levels may sometimes be requested when a patient shows signs of malnutrition or malabsorption or is known to have a disorder that affects nutrient absorption. When a breastfed infant has a vitamin B12 or folate deficiency, then the mother may also be tested to see if she has a deficiency that is affecting both her and her child. When a patient is being treated for a vitamin B12 or folate deficiency, s/he may occasionally be monitored to evaluate the effectiveness of the treatment. In a person with a nutritional deficiency, this may be done as a follow-up to treatment. In a person with a condition causing a chronic deficiency, this may be part of a long term treatment plan.
What does the test result mean?
The doctor is looking for vitamin B12 and/or folate deficiencies. If a symptomatic patient has decreased concentrations of vitamin B12 and/or folate, then it is likely that they have some degree of deficiency. The test results will indicate the presence of the deficiency, but they do not necessarily reflect the severity of the anaemia or neuropathy associated with the deficiency or its underlying cause.
There are a variety of causes of vitamin B12 and/or folate deficiencies. They include:
Insufficient intake
The human body stores several years worth of vitamin B12 in the liver and it is readily available in the food supply, so a dietary deficiency of this vitamin should be rare in Australia. It may be seen sometimes with general malnutrition, and in vegans - those who do not consume any animal products including milk and eggs. It may also be seen in children of vegans and breastfed infants. Since they do not have the stores that adults do, deficiencies in children and infants show up fairly quickly.
Folate used to be a common deficiency but with the advent of fortified cereals, breads, and grain products it is less common today. Since folate is stored in tissue in smaller quantities than vitamin B12, folate must be consumed more regularly.
Malabsorption
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 (an intolerance to gluten present in wheat and other cereal that causes inflammation and malabsorption)
- Bacterial overgrowth in the stomach and intestines
- Reduced stomach acid production (stomach acid is necessary to separate vitamin B12 from the protein in food)
- Pernicious anaemia, is occasionally the cause of vitamin B12 deficiency. Normally a molecule called intrinsic factor is made by parietal cells that line the stomach. Vitamin B12 binds to intrinsic factor in the stomach, then the resulting compound is absorbed in the intestines. With pernicious anaemia, little or no intrinsic factor is produced, preventing the absorption of vitamin B12.
- Surgery that removes part of the stomach (and the parietal cells) or the intestines may greatly decrease absorption
Increased loss - this may be seen with:
- Liver and kidney disease
- Alcoholism, with alcohol
- Anti-seizure medications such as phenytoin can lower folate as can drugs such as metformin and methotrexate
Increased need
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 birth defects in the child.
If a patient with a vitamin B12 or folate deficiency is being treated with supplements (or with vitamin B12 injections), then normal or elevated results indicate a response to treatment.
Is there anything else I should know?
If a patient is deficient in both vitamin B12 and folate, but only takes folic acid supplements, the vitamin B12 deficiency may be masked. The anaemia associated with both may be resolved, but the underlying neuropathy (nerve damage) will persist.
The Schilling test was once used fairly routinely to confirm a diagnosis of pernicious anaemia as the cause of a vitamin B12 deficiency. It has fallen from favour because it involves the administration of radioactive vitamin B12. The Schilling test has been replaced, in part, by the measurement of intrinsic factor binding antibodies and parietal cell antibodies.
Vitamin B12 exists in our body in two forms:
- Bound to haptocorrin which is considered the storage form of vitamin B12
- Bound to transcobalamin for transport to the cells (Active B12)
Common Questions
Ask a Laboratory Scientist
Article Sources
NOTE: This article is based on research that utilizes the sources cited here as well as the collective experience of the Lab Tests Online Editorial Review Board. This article is periodically reviewed by the Editorial Board and may be updated as a result of the review. Any new sources cited will be added to the list and distinguished from the original sources used.
Ross D Brown, Mark R Langshaw, Elaine J Uhr, John N Gibson and Douglas E Joshua
The impact of mandatory fortification of flour with folic acid on the blood folate levels of an Australian population. MJA 20011;194(2):65-67
