The Test Sample
What is being tested?
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.
How is the sample collected for testing?
A blood sample is obtained by inserting a needle into a vein in the arm.
NOTE: If undergoing medical tests makes you or someone you care for anxious, embarrassed, or even difficult to manage, you might consider reading one or more of the following articles: Coping with Test Pain, Discomfort, and Anxiety, Tips on Blood Testing, Tips to Help Children through Their Medical Tests, and Tips to Help the Elderly through Their Medical Tests.
Another article, Follow That Sample, provides a glimpse at the collection and processing of a blood sample and throat culture.
Is any test preparation needed to ensure the quality of the sample?
The blood sample is usually collected in the morning after an overnight fast, preferably before taking any medication. People may be asked to attend their local hospital for the test, as the blood sample has to be delivered to the laboratory very quickly to be preserved.