To detect vitamin A deficiency or toxicity
When you have symptoms suggesting a vitamin A deficiency or excess, or are at risk for a deficiency
A blood sample drawn from a vein in your arm
Fasting is required and no alcohol should be consumed for 24 hours before sample collection.
This test measures the level 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 worth stored. 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.
Deficiencies in vitamin A are rare in the United States, but they are a major health problem in many developing nations where high numbers of people have limited diets. One of the first signs 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 Organization 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 levels that reflected an inadequate supply of vitamin A.
In the U.S., deficiencies are primarily seen in those with malnutrition, with malabsorption disorders such as celiac 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 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. Retinol and vitamin A are light-sensitive, so the sample will be protected from light after it is collected to prevent falsely low levels.
Is any test preparation needed to ensure the quality of the sample?
Fasting is required and no alcohol consumption for 24 hours before sample collection. Recent alcohol consumption may result in falsely elevated vitamin A levels.
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 and who are at risk of vitamin A deficiency. Testing for this purpose is not common because vitamin A deficiencies are rare in the United States. Sometimes testing may be used to detect toxic levels caused by ingestion of large amounts of vitamin A.
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.
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). 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.
When is it ordered?
- 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 done periodically when a person has a disease that is associated with malabsorption of nutrients to monitor vitamin A status and ensure that the person is getting sufficient vitamin A. Some diseases that are associated with inadequate vitamin A absorption include:
Testing may be performed when a person has signs and symptoms that suggest vitamin A toxicity and the person's medical history is consistent with consumption of foods or vitamin supplements containing vitamin A. Some of the signs and symptoms associated with vitamin A toxicity are:
- Nausea and vomiting
- Double or blurred vision
- Muscle pain
- Bone and joint pain
- Weight loss
- Hair loss
- Mucous membrane dryness
- 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 blood level indicates that a person currently has sufficient vitamin A but does not indicate how much is stored in reserve. The body will maintain vitamin A in the blood at a relatively stable level until stores are depleted.
A low vitamin A blood test result indicates that all reserves have been depleted and the person is deficient.
A high vitamin A blood level 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?
People 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 is prevalent in many parts of the world during pregnancy.
Eating excessive amounts of foods with beta carotene, 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 are the dietary sources of vitamin A?
Sources of preformed vitamin A include meat (especially liver), eggs, dairy products, and fortified foods. Sources of carotene (mainly beta carotene) include brightly colored fruits and vegetables such as carrots, spinach, apricots, sweet potatoes, and cantaloupe.
What are the recommended dietary allowances (RDA) for vitamin A?
For teens and adults age 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.
How are vitamin A deficiencies treated?Mild to moderate deficiencies are treated with supplements and/or with alterations in diet. More severe deficiencies may require monitored therapeutic doses of vitamin A.
Can vitamin A testing be done in my doctor's office?
On This Site
Elsewhere On The Web
Office of Dietary Supplements: Dietary Supplement Fact Sheet, Vitamin A and Carotenoids
Familydoctor.org: Vitamins and Minerals, How to Get What You Need
MedlinePlus Medical Encyclopedia: Vitamin A