B Vitamins

Also Known As

Vitamin B complex

Thiamine or thiamin (B1)

Riboflavin (B2)

Niacin (B3)

Pantothenic acid (B5)

Pyridoxal phosphate (B6)

Biotin (B7)

Formal Name

Vitamin B Testing

This article was last reviewed on

July 27, 2020.

This article waslast modified on September 10, 2020.

At a Glance

Why Get Tested?

To screen for and detect moderate to severe vitamin B deficiencies

When To Get Tested?

When you have symptoms that may be due to a B vitamin deficiency, are at risk for a deficiency, or have a condition associated with malabsorption

Sample Required?

A blood sample drawn from a vein in your arm; a random or 24-hour urine sample may also be collected.

Test Preparation Needed?

No special preparation is usually needed. However, you may be instructed to fast overnight and/or avoid taking vitamin supplements for a certain time period before the specimen is drawn for some vitamin B tests.

You may be able to find your test results on your laboratory's website or patient portal. However, you are currently at Lab Tests Online. You may have been directed here by your lab's website in order to provide you with background information about the test(s) you had performed. You will need to return to your lab's website or portal, or contact your healthcare practitioner in order to obtain your test results.

Lab Tests Online is an award-winning patient education website offering information on laboratory tests. The content on the site, which has been reviewed by laboratory scientists and other medical professionals, provides general explanations of what results might mean for each test listed on the site, such as what a high or low value might suggest to your healthcare practitioner about your health or medical condition.

The reference ranges for your tests can be found on your laboratory report. They are typically found to the right of your results.

If you do not have your lab report, consult your healthcare provider or the laboratory that performed the test(s) to obtain the reference range.

Laboratory test results are not meaningful by themselves. Their meaning comes from comparison to reference ranges. Reference ranges are the values expected for a healthy person. They are sometimes called "normal" values. By comparing your test results with reference values, you and your healthcare provider can see if any of your test results fall outside the range of expected values. Values that are outside expected ranges can provide clues to help identify possible conditions or diseases.

While accuracy of laboratory testing has significantly evolved over the past few decades, some lab-to-lab variability can occur due to differences in testing equipment, chemical reagents, and techniques. This is a reason why so few reference ranges are provided on this site. It is important to know that you must use the range supplied by the laboratory that performed your test to evaluate whether your results are "within normal limits."

For more information, please read the article Reference Ranges and What They Mean.

What is being tested?

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.

B vitamin deficiencies can occur when:

There is an inadequate supply of B vitamins.
You are unable to absorb or utilize one or more of the vitamins.
You eat foods or take drugs that slow or prevent the absorption, production or 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., B vitamin deficiencies are primarily seen in people with general malnutrition, chronic alcoholism, malabsorption or digestive disorders (e.g., celiac disease), those who have had gastric bypass surgery, and in the elderly. They are also sometimes seen with other chronic diseases, with cancer and cancer treatment, with use of medicines that interfere with the breakdown and use of vitamins, with special diets, and with diarrhea that lasts more than a few days to weeks.

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 nonspecific, especially with mild to moderate deficiencies. Individuals often have multiple vitamin deficiencies, so they may also have a wide variety of symptoms. Common deficiency symptoms include a rash, dermatitis, red, swollen 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, lipid, and alcohol metabolism, and is required for the proper functioning of the nervous system, heart, and muscles.

Sources: Whole grains and fortified bread, cereal, pasta, and rice; Meat (especially pork) and fish; Legumes (such as black beans and soybeans), seeds, and nuts

Deficiency: Found primarily with chronic alcoholism, HIV/AIDS, diabetes, those who have had bariatric surgery and older individuals. Some medicines such as furosemide and 5-fluorouracil can lower thiamin levels in the body. Thiamin deficiency can cause loss of weight and appetite, confusion, memory loss, muscle weakness, and heart problems. It causes Wernicke-Korsakoff syndrome, which mostly affects people with alcoholism, with tingling and numbness in the hands and feet, severe memory loss, disorientation, and confusion. Less commonly, severe thiamin deficiency leads to a disease called beriberi.

Test name: Thiamine (Thiamine diphosphate) in blood
Other ways to measure: Transketolase (functional thiamine test)

B2, Riboflavin

Also known as: Vitamin G

Role: B2 is a coenzyme involved in energy production, cellular function, growth, and development; and metabolism of fats, drugs, and steroids, and is required for the metabolism of other B vitamins. In addition, riboflavin helps maintain normal levels of homocysteine, an amino acid in the blood.

Sources: Eggs, organ meats (such as kidneys and liver), lean meats, and low-fat milk; Green vegetables (such as asparagus, broccoli, and spinach); Fortified cereals, bread, and grain products

Deficiency: Called ariboflavinosis, usually seen along with other vitamin deficiencies in those with alcoholism, malabsorption, liver disease, in the elderly, vegetarians (especially strict vegetarians who avoid dairy foods and eggs), pregnant women and breastfeeding women and their babies. Riboflavin deficiency can cause skin disorders, sores at the corners of your mouth, swollen and cracked lips, hair loss, sore throat, liver disorders, and problems with reproductive and nervous systems. Severe, long-term riboflavin deficiency can cause anemia and cataracts.

Test name: Riboflavin, blood or urine
Other ways to measure: Glutathione reductase in erythrocytes (activity)

B3, Niacin

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: Meats, such as poultry, beef, pork, and fish; Some types of nuts, legumes, and grains; Enriched and fortified foods, such as many breads and cereals

Deficiency: Seen in undernourished people with AIDS, alcohol use disorder, anorexia, inflammatory bowel disease, or liver cirrhosis; with carcinoid syndrome, a condition in which slow-growing tumors develop in the digestive tract. Severe niacin deficiency leads to a disease called pellagra, classic symptoms are dermatitis (rough skin that turns red or brown in the sun), a bright red tongue, vomiting, constipation or diarrhea, depression, headaches, extreme tiredness, aggressive, paranoid, suicidal behavior, hallucinations, apathy, loss of memory

Toxicity: Pharmacologic doses can cause flushing, headaches, low blood pressure, high blood sugar levels, blurred or impaired vision and fluid buildup in the eyes. High doses may damage liver.

Test name: Niacin and metabolites in blood or urine; N1-Methylnicotinamide, N1-methyl-2-pyridone-5-carboxamide in urine thought to be the most reliable measure of intake and body status
Other ways to measure: measured as NAD (Nicotinamide adenine dinucleotide) in blood or urine

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. However, people with a rare inherited disorder called pantothenate kinase-associated neurodegeneration can't use pantothenic acid properly. This disorder can lead to symptoms of pantothenic acid deficiency, associated with "burning feet" and impaired wound healing.

Test name: Pantothenic acid in blood or urine

B6, 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: Poultry, fish, and organ meats; Potatoes and other starchy vegetables; Fruit (other than citrus)

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, kidney malfunction, autoimmune disorders and in those who take certain antiepileptic drugs and theophylline. Deficiency can cause anemia, itchy rashes, scaly skin on the lips, cracks at the corners of the mouth, a swollen tongue, depression, confusion, and a weak immune system. Infants who do not get enough vitamin B6 can become irritable or develop extremely sensitive hearing or seizures. Overdosing can cause severe nerve damage, leading people to lose control of their bodily movements.

Test name: Pyridoxal phosphate (PLP) in blood
Other ways to measure: Vitamin B6 functional test, Urine 4-pyridoxic acid, urine xanthurenic acid

B7, Biotin

Also known as: Vitamin H, Coenzyme R, Biopeiderm

Role: B7 is a coenzyme that is necessary for fat, protein, and carbohydrate metabolism and plays a role in hormone production.

Sources: Meat, fish, eggs, and organ meats (such as liver); Seeds and nuts; Certain vegetables (such as sweet potatoes, spinach, and broccoli). B7 is also made by intestinal bacteria.

Deficiency: Very rare; may occur in those receiving total parenteral nutrition, with chronic alcohol abuse, and with some inborn errors of metabolism, such as "biotinidase deficiency"; deficiency of biotin can cause thinning hair and loss of body hair; a rash around the eyes, nose, mouth, and anal area; pinkeye; seizures; skin infection; brittle nails; and nervous system disorders. Symptoms of biotin deficiency in infants include weak muscle tone, sluggishness, and delayed development. Biotin has not been shown to cause any harm. However, supplements that contain biotin may cause false results in many lab tests, including but not limited to cardiovascular diagnostic tests and hormone tests.

Test names: Biotin in blood
Other ways to measure: Urinary 3-hydroxyisovalerate excretion

B12, Cobalamin

See the article on Vitamin B12 and Folate

B9, Folic Acid or Folate

Also known as: Vitamin B9, Vitamin M
See the article on Vitamin B12 and Folate

Common Questions

How is the test used?

One or more B vitamin tests may be used to diagnose deficiencies if you have typical symptoms.

B vitamin toxicity rarely occurs so testing is not often done for this purpose. High concentrations of a few of the B vitamins may affect the liver or nervous system.
When is it ordered?
Testing is primarily ordered when you have signs and symptoms that may be due to a B vitamin deficiency. Signs and symptoms depend on the vitamins that are deficient. Examples of some of the common ones include:

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)

Anemia

Fatigue, insomnia

Irritability, difficulty with memory, depression

Testing may also be ordered when you have a condition that puts you at risk of B vitamin deficiencies. Examples of these conditions include:

A limited or inadequate diet

Malnutrition

Being given nutrition intravenously (parenteral nutrition)

Taking a drug that interferes with absorbing, using or breaking down vitamin B

Gastric bypass surgery

Alcoholism

Chronic diseases associated with malabsorption, such as celiac disease
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.

If test results are normal, then it is more likely that your 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 taking high doses of the vitamin supplements.
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 you 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 your 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?

In general, no. These are specialized tests that need to be performed in a laboratory and may need to be sent to a reference laboratory.

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