To detect vitamin A deficiency or toxicity
When a person has symptoms suggesting vitamin A deficiency or excess, or is at risk of vitamin deficiency such as patients on nutrition supplements.
A blood sample taken from a vein in your arm
A fasting blood sample is required, and no alcohol should be consumed for 24 hours before sample collection.
This test measures the concentration of retinol in the blood; retinol is the primary form of vitamin A in animals. Vitamin A is an essential nutrient required for healthy vision, skin growth and integrity, bone formation, immune function, and embryonic development. It is required to produce photoreceptors in the eyes and to maintain the lining of the surface of the eyes and other mucous membranes. Deficiencies in vitamin A can impair night vision, cause eye damage, and in severe cases lead to blindness. Acute or chronic excesses of vitamin A can be toxic, cause a range of symptoms, and sometimes lead to birth defects.
The body cannot make vitamin A and must rely on dietary sources of vitamin A. Meat sources provide vitamin A (as retinol), while vegetable and fruit sources provide carotene (a substance that can be converted into vitamin A by the liver). Vitamin A is stored in the liver and fat tissues (it is fat-soluble), and healthy adults may have as much as a year's requirement stored, whereas a child liver may have enough stores to last only for several weeks. The body maintains a relatively stable concentration in the blood through a feedback system that releases vitamin A from storage as needed and increases or decreases the efficiency of dietary vitamin A absorption.
Vitamin A can be mobilised from the liver to peripheral tissues. In blood, it carried by a protein called retinol-binding protein (RBP). Retinol is taken up by the peripheral tissue from the complex. Therefore, the liver’s capacity to produce RBP also affects vitamin A level at the time of blood testing.
Deficiencies in vitamin A are rare in the United Kingdom, but they are a major health problem in many developing countries where high numbers of people have limited diets. One of the first symptoms of vitamin A deficiency is night blindness. In a 1995-2005 review of the global prevalence of vitamin A deficiency in populations at risk, the World Health Organisation estimated that night blindness affected as many as 5 million preschool age children and nearly 10 million pregnant women. In addition to this, they estimated that another 190 million preschool age children and 19 million pregnant women were at risk of vitamin A deficiency, with low retinol concentrations that reflected an inadequate supply of vitamin A. In these countries, a low vitamin A is most strongly associated with health consequences during periods of high nutritional demands such as pregnancy, illnesses and lactation.
In the UK, deficiencies are primarily seen in those with malnutrition, with malabsorption disorders such as coeliac disease, cystic fibrosis, or chronic pancreatitis, in the elderly, and in those with alcoholism and liver disease.
Vitamin A toxicity occurs primarily from overuse of vitamin supplements. However, it can sometimes occur when the diet includes a high proportion of foods from animal sources that are high in vitamin A, such as liver.
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?
A fasting blood sample is required and no alcohol should be consumed for 24 hours before sample collection.
How is it used?
Vitamin A testing is used to help diagnose vitamin A deficiency in people with symptoms, such as night blindness, or in people with diseases that impair intestinal absorption of nutrients. It may be used to monitor blood concentrations in people with known vitamin A deficiency who are receiving supplements. It may also be used to detect toxic concentrations caused by ingestion of large amounts of vitamin A.
When is it requested?
A vitamin A test may be requested when a person has symptoms that suggest vitamin A deficiency or general malnutrition. These symptoms include:
- Night blindness
- Dry eyes, skin, and hair
- Ulcers and damage to the cornea (the outermost layer of the front of the eye that covers the iris and pupil)
- Skin thickening and lesions
- Grayish spots on eye lining (Bitot spots)
- Repeated infections
Testing may be performed when a person has a disease that is associated with malabsorption of nutrients to monitor vitamin A status. Testing may be done periodically to ensure that the person is obtaining sufficient vitamin A. Some diseases that are associated with inadequate vitamin A absorption include:
- Coeliac disease
- Irritable bowel syndrome
- Patients undergone small-bowel bypass surgery
- Pancreatic insufficiency
- Chronic pancreatitis
- Crohn’s disease
- Liver disease and cirrhosis
- Cystic fibrosis
Chronic alcohol excess also affects vitamin A absorption. Alcohol impedes the affinity of an enzyme called alcohol dehydrogenase which impairs the conversion of retinol to retinoic acid, thus reducing its absorption.
Testing may be performed when a person has symptoms that suggest vitamin A toxicity and their medical history is consistent with consumption of foods or vitamin supplements containing vitamin A. Excess vitamin A can have significant toxicity (also called hypervitaminosis A), but large amounts of beta carotene and carotenoids (similar in structure to vitamin A, used to turn people orange who have skin condition that are light sensitive) are not usually associated with major side effects. The symptoms of hypervitaminosis A can be acute due to sudden and excessive consumption of vitamin A. Normally the features of toxicity that are seen are due to chronic excessive intake. This is as a result of preformed vitamin A from supplements and therapeutic retinoids (similar in structure to vitamin A) rather due to dietary vitamin A excess.
Some of the symptoms associated with acute hypervitaminosis A are:
- Headache in adults
- Nausea and vomiting
- Double or blurred vision
- Peeling of the skin
- Bulging fontanelles (soft spot on the baby's head) in infants
Symptoms of chronic hypervitaminosis A include:
- Liver enlargement
- Muscle pain
- Bone and joint pain
- Weight loss
- Hair loss
- Mucous membrane dryness
- Dry itchy skin
- Liver dysfunction
- Cracks (fissures) at the corners of the mouth
- Inflammation of the tongue (glossitis)
What does the test result mean?
A normal vitamin A concentration indicates that a person currently has sufficient vitamin A but the result does not indicate how much is stored in reserve. The body will maintain vitamin A in the blood at a relatively stable concentration until stores are depleted. A low vitamin A test result indicates that all reserves have been depleted and the person is deficient. The result is dependent on several factors, including retinol binding protein production in the liver, infection, nutrition status, and existing level of other nutrients such as iron and zinc. Medications such as allopurinol, cholestyramine, colestipol and neomycin can decrease vitamin A level in the blood while oral contraceptive use can increase vitamin A.
A high vitamin A concentration typically indicates that the capacity to store vitamin A has been exceeded and excess vitamin A is now circulating in the blood and may be deposited in other tissue, leading to toxicity.
Is there anything else I should know?
A person with a minimal amount of vitamin A stored may have marginal but adequate vitamin A until they have an illness or other condition, such as pregnancy, that puts increased demands on their body. This is one of the reasons that night blindness during pregnancy is prevalent in many parts of the world. However, requirement in pregnancy should be balanced. There is a possibility of increased risk of neurological complications and other malformations resulting from excessive use of vitamin A shortly before and during pregnancy.
In measles outbreaks, rare in the UK due to vaccination, vitamin A has been shown to be helpful for symptoms in children and reduces death rate in those less than 2 years old.
Eating excessive amounts of foods with beta carotene (carotenoids are related in structure to vitamin A), such as carrots, can cause a person's skin to turn yellow-orange but it does not cause vitamin A toxicity. The body does not convert beta carotene to vitamin A when there is sufficient vitamin A present.
What is vitamin A?
There are 3 essential forms of vitamin A: retinols, beta- carotenes and carotenoids. Retinol is also known as preformed vitamin A, is the most active form and is mostly found in animal sources of food. Beta-carotene is known as provitamin A and is the plant source of retinol from which mammals make two-thirds of their vitamin A. Carotenoids are the largest group of the 3, and exist in free alcohol or in fatty acyl-ester form.
What are the dietary sources of Vitamin A?
Concentration of vitamin A is highest in liver and fish oils. Other sources of preformed vitamin A include milk, eggs, dairy products, and fortified foods. Sources of carotene (mainly beta carotene) include brightly coloured fruits and vegetables such as carrots, spinach, apricots, sweet potatoes, tomato and cantaloupe.
What are the recommended dietary allowances (RDA) for vitamin A?
For teenagers and adults aged 14 and older, the RDA is 900 micrograms (mcg) (3,000 IU) for males and 700 mcg (2,310 IU) for females. The recommendations for others, such as infants, children and pregnant women, vary. For these, see the lists provided by the National Institutes of Health Office of Dietary Supplements.
The requirement for vitamin A can be increased in sick children. The World Health Organisation (WHO) and UNICEF have issued a joint statement recommending that vitamin A is administered to all children, especially if they are below 2 years and diagnosed with measles.
How is vitamin A deficiency treated?
Can vitamin A testing be done at my doctor's surgery?
No, this test requires specialised equipment and is not offered by every laboratory. In many cases, your blood will be sent to a reference laboratory (provides specialist testing and interpretation). There are also special requirements for sample collection and processing. Your local laboratory will provide details for your healthcare professional. One such requirement is that the sample must be protected from light once it has been taken, and continue to be protected until it arrives in the laboratory.
On This Site
Tests: Full blood count (FBC), Vitamin B12 and Folate, Vitamin D, Iron Tests, Retinol-Binding Protein (RBP)
Conditions: Malnutrition, Coeliac Disease, Cystic Fibrosis, Pancreatitis, Anaemia, Alcoholism, Liver Disease, Malabsorption
Elsewhere On The Web
ACB, Analyte Monographs (AMALC): Vitamin A
NHS: Vitamins and Minerals
World Health Organization: Safe vitamin A dosage during pregnancy and lactation: recommendations and report of a consultation
GOV.UK: Vitamin A, A migrant health guide
Cochrane Methods Equity: Vitamin A for measles
Cochrane: Antioxidant supplements for prevention of mortality in healthy participants and patients with various diseases