To screen for and detect moderate to severe vitamin B deficiencies
Fasting is usually required for blood testing.
The B vitamins are nutrients that the body requires in small amounts (micronutrient) for metabolism, energy production, and for cell, skin, bone, muscle, organ, and nervous system health. B vitamin tests measure these specific compounds in the blood or urine 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. Severe B vitamin deficiencies are rare in the United States but are still prevalent in areas of the world with diet deficiencies.
Deficiencies can occur when:
- There is an inadequate supply of B vitamins.
- Someone is unable to absorb or utilize 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 U.S., deficiencies are primarily seen in those with general malnutrition, chronic alcoholism, in people with malabsorption or digestive disorders, as may be seen with gastric bypass surgery and Celiac 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 diarrhea. 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 – a 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, numbness, tingling or burning in the hands or feet, anemia, fatigue, 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.
The B vitamins include:
|B1, Thiamine or thiamin
Also known as: Vitamin F, Aneurin, Thiamine diphosphate (TDP) – physiologically active form
Role: B1 is a coenzyme that helps the body produce energy, 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, pork, seafood, nuts, legumes
Deficiency: In U.S., found primarily with chronic alcoholism. Can cause:
Test name: Thiamine (Thiamine diphosphate) in blood
Also known as: Vitamin G
Role: B2 is a coenzyme involved in energy production and is required for the metabolism of other B vitamins
Sources: Cereals and whole grains, green leafy vegetables, lean meats, dairy products, eggs, enriched breads.
Deficiency: Called ariboflavinosis, usually seen along with other vitamin deficiencies in those with alcoholism, malabsorption, liver disease, and in the elderly.
Test name: Riboflavin, blood or urine
Also known as: Nicotinic acid, Nicotinamide, Vitamin P, Vitamin PP
Role: B3 is involved in enzyme reactions, metabolism, and energy production. It is given in pharmacologic doses to lower LDL-cholesterol and triglycerides and raise HDL-cholesterol
Sources: B3 is found in lean meats, eggs, fish, whole grain cereals and legumes.
Deficiency: Severe deficiency in conjunction with a low-protein diet causes: Pellagra - classic symptoms are dermatitis, diarrhea, and dementia; may also cause a rash in areas exposed to the sun.
Deficiencies also seen with alcoholism, cirrhosis, Hartnup disease, Crohn disease, and carcinoid syndrome. Niacin synthesis requires adequate B6, B2, iron, and copper. Up to 60% of niacin is synthesized from tryptophan.
Toxicity: Pharmacologic doses can cause flushing and headaches. High doses may affect liver.
Test name: Niacin metabolites: N1-Methylnicotinamide, 2-Pyridone in urine thought to be the most reliable measure of intake and body status
|B5, Pantothenic acid
Role: B5 helps 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
|B6, Pyridoxal Phosphate (PLP)
Three main forms: Pyridoxine, pyridoxamine, and pyridoxal
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 alcoholism, 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)
Also known as: Vitamin H, Vitamin B-w
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, weakness.
Test names: Biotin in urine
See the article on Vitamin B12 and Folate
|Folic Acid or Folate
Also known as: Vitamin B9, Vitamin M
How is the sample collected for testing?
Is any test preparation needed to ensure the quality of the sample?
Fasting is usually required for blood testing.
How is it used?
One or more B vitamin tests may be used to screen for and detect deficiencies in people 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 individuals 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 for those with alcoholism or with chronic diseases associated with malabsorption, such as Celiac disease.
When is it ordered?
- 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)
- Fatigue, insomnia
- Irritability, difficulty with memory, depression
B vitamin testing may be used when a person has a condition that puts them at risk for a deficiency. Those at increased risk include people who are malnourished, are chronic alcoholics, or who have a condition such as Celiac disease that is associated with malabsorption.
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 someone is deficient, the person often has 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 level may be associated with vitamin toxicity. This rarely occurs and when it does, it is usually due to exposure to high doses of the vitamin.
Is there anything else I should know?
A person may sometimes 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 healthcare provider suspects a B1 deficiency, the provider may prescribe B vitamin supplements and then monitor the person to see if 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 an adequate amount of B vitamins are provided in the diet, blood levels will remain relatively stable. If you are deficient, your healthcare provider may want you to supplement your B vitamins but talk to your provider before taking this step.
Should everyone have their B vitamin levels checked?
Most people have adequate B vitamins and will not need testing unless they develop a condition that puts them at risk of a B vitamin deficiency.
Can B vitamins be measured at home or in my doctor's office?