To screen for and detect moderate to severe vitamin B deficiencies
When someone has symptoms that may be due to a B vitamin deficiency, is at risk for a deficiency, or has a condition associated with malabsorption. However, most people at risk are treated with vitamin B complex and do not require testing.
A blood sample taken from a vein in your arm.
The blood sample is usually collected in the morning after an overnight fast, and preferably before taking any medication.
The B vitamins are nutrients that the body requires in small amounts (micronutrients) for metabolism, energy production, and for cell, skin, bone, muscle, organ, and nervous system health. Vitamin B tests measure some of these specific compounds in the blood to help evaluate a person's nutritional status.
B vitamins are absorbed from the diet, used as needed, and any excess is removed from the body through the urine. Because B vitamins are water-soluble, only small amounts are stored by the body and they must be obtained from foods rich in B vitamins or from supplements on a regular basis. Many foodstuffs, such as cereals, are fortified with B vitamins in developed countries. Severe B vitamin deficiencies are rare in the United Kingdom but are still prevalent in areas of the world with dietary deficiencies.
Deficiencies can occur when:
- There is an inadequate supply of B vitamins in the diet.
- Someone is unable to absorb or utilise one or more of the vitamins.
- A person eats foods that inhibit the action of a vitamin.
- A deficiency in another vitamin or mineral prevents its use.
- The need for the vitamin is increased.
In the UK, deficiencies are primarily seen in those with general malnutrition, chronic alcohol dependence, in people with malabsorption or digestive disorders, as may be seen with gastric bypass surgery and coeliac disease, and in the elderly. They are also sometimes seen with other chronic diseases, with cancer and cancer treatment, with fad diets, and with prolonged diarrhoea. Pregnant women with a limited diet can be at an increased risk for B vitamin deficiencies and so can their babies. Rarely, a baby may have an inborn error of metabolism – an inherited condition that prevents the proper use of a B vitamin.
Symptoms associated with B vitamin deficiencies can be seen in characteristic groups but may also be nonspecific, especially with mild to moderate deficiencies. Since an affected person often has multiple vitamin deficiencies, they may also have multiple symptoms. Common deficiency symptoms include a rash, dermatitis, inflamed tongue, soreness of the angles of the mouth, numbness, tingling or burning in the hands or feet, anaemia, fatigue, insomnia and mental changes.
B vitamin toxicity rarely occurs, usually when someone ingests much more than the recommended dose of supplements. High concentrations of a few of the B vitamins may affect the liver or nervous system.
Name: Thiamine or thiamin
Also known as: Also known as: aneurin, thiamine diphosphate (TDP, the physiologically active form)
Role: B1 is a coenzyme that helps the body produce energy. It is involved in glucose, amino acid, and alcohol metabolism, and is required for the proper functioning of the nervous system, heart, and muscles.
Sources: cereals and whole grains, potatoes, yeast, pork, seafood, nuts, legumes
Deficiency: In UK, found primarily with chronic alcohol dependence. Can cause:
Test name: thiamine (thiamine diphosphate) in blood
Role: B2 is a coenzyme involved in energy production and is required for the metabolism of other B vitamins and for fatty acid oxidation.
Sources: cereals and whole grains, green leafy vegetables, lean meats, dairy products, eggs, enriched breads.
Test name: riboflavin, in blood
Role: B3 is involved in enzyme reactions, metabolism, and energy production.
Sources: B3 is found in lean meats, eggs, fish, whole grain cereals and legumes. Up to 60% of niacin is synthesized in the body from the amino acid tryptophan.
Deficiency: severe deficiency in conjunction with a low-protein diet causes pellagra. Symptoms include irritability, dermatitis, diarrhea, and dementia and a rash in areas exposed to the sun.
Deficiencies are also seen with alcohol dependence, cirrhosis, Hartnup disease, Crohn disease, and carcinoid syndrome. Niacin synthesis in the body requires adequate B6, B2, iron, and copper.
Toxicity: pharmacological doses can cause flushing and headaches. High doses may affect the liver.
Test name: niacin metabolites: N1-methylnicotinamide, 2-pyridone in urine are thought to be the most reliable indicators of intake and body status but are measured only for research purposes.
Name: Pantothenic acid
Role: B5 required to break down and use fats, proteins, and carbohydrates.
Sources: most foods
Deficiency: B5 deficiency is rare as it is widely distributed in foods. Associated with "burning feet" and impaired wound healing.
Test name: pantothenic acid in blood or urine, used only for research purposes
Name: Pyridoxal phosphate (PLP)
Role: B6 is a coenzyme involved in amino acid metabolism and hemoglobin synthesis. It is also necessary for the nervous system and immune system.
Sources: pork, fish, chicken, bananas, wheat germ, legumes.
Deficiency: B6 deficiency is rare by itself; adequate B2 is required for the formation of active PLP; may be seen with chronic alcohol dependence, malabsorption, smoking, and in asthmatics who take theophylline; can cause convulsions and decreased immunity. Both deficiency and toxicity can cause peripheral neuropathy.
Test name: pyridoxal phosphate (PLP)
Role: B7 is a coenzyme that is necessary for fat, protein, and carbohydrate metabolism and plays a role in hormone production.
Sources: soy, egg yolks, peanuts, legumes, bananas, and grapefruit. B7 is also made by intestinal bacteria.
Deficiency: very rare; may occur in those receiving total parenteral nutrition and with some inborn errors of metabolism; can cause weakness, delayed development, rash, hair loss.
Test names: biotin and biotin metabolites in urine or blood, mostly used for research purposes.
How is it used?
One or more B vitamin tests may be used to screen for and detect deficiencies in those with characteristic symptoms.
Testing may also be used for those who have a condition that puts them at risk of B vitamin deficiencies. This may include those with a limited or inadequate diet, those with signs of malnutrition, those being given their nutrition intravenously (parenteral nutrition), and those who have had gastric bypass surgery. Testing may also be performed on those with alcohol dependence or with chronic diseases associated with malabsorption, such as coeliac disease.
Tests for B vitamins (apart from B12 and folate) are rarely required for clinical purposes, as treatment with vitamin B complex is safe and cheap; most people are treated without being tested beforehand. Testing is more often undertaken for people taking part in clinical trials related to nutrition.
When is it requested?
Tests may be requested when someone is poorly nourished and also has symptoms that may be due to a B vitamin deficiency. Signs and symptoms depend on the vitamins that are deficient. Some of the common ones include:
- unexplained rash, dermatitis
- inflamed tongue, sores on the lips or in the mouth, cracks at the corners of the mouth
- numbness, tingling or burning in the hands or feet (peripheral neuropathy)
- irritability, difficulty with memory, depression
B vitamin testing may rarely be useful when a person has a condition that puts them at risk for a deficiency. Those at increased risk include people who are malnourished, are dependent on alcohol, or who have a condition such as coeliac disease that is associated with malabsorption. However, many people with these conditions are prescribed supplements to prevent deficiences so do not require testing.
B vitamin toxicity rarely occurs so testing for this purpose is not often done. High concentrations of a few of the B vitamins may affect the liver or nervous system.
What does the test result mean?
Test results that are low may indicate a B vitamin deficiency but will not reveal whether it is due to an inadequate supply or an inability to absorb or use available B vitamins. When a person is deficient, they often have multiple vitamin deficiencies.
If test results are normal, then it is more likely that a person's symptoms are due to another cause.
A high B vitamin concentration may be associated with vitamin toxicity. This rarely occurs and when it does, it is usually due to exposure to high doses of vitamin supplements.
Is there anything else I should know?
A person will usually be diagnosed and treated for a B vitamin deficiency based upon clinical findings and a response to treatment, rather than testing. For instance, if a doctor suspects a B1 deficiency, he/she may prescribe B vitamin supplements and then monitor the patient to see if the symptoms resolve.
What are the Recommended Dietary Allowances (RDA) for B vitamins?
The RDA for adults, children, and other groups vary by the specific B vitamin. To determine the RDA for a particular vitamin, see the Dietary Reference Intakes tables provided online by the Office of Dietary Supplements.
Can I change my B vitamin levels?
In general, your body will use the amount of B vitamins that it needs and eliminate any excess from the body. As long as adequate amounts of B vitamins are provided in the diet, concentrations in the blood will remain relatively stable. If you are deficient, your doctor may ask you to take vitamin B supplements, but talk to your doctor before taking this step.
Should everyone have their B vitamin levels checked?
Can B vitamins be measured at home or in my doctor's surgery?
On This Site
Tests: Vitamin B12 and Folate
Conditions: Alcoholism, Coeliac Disease, Malnutrition, Vitamin B12 Deficiency, Malabsorption
Elsewhere On The Web
European Food Information Council: Vitamins
British Nutrition Foundation: Nutrient requirements
Net Doctor UK: Vitamins and Minerals
NHS: Vitamins and Minerals