Vitamin A
At a Glance
Why Get Tested?
To detect vitamin A deficiency or toxicity
When to Get Tested?
When a person has symptoms suggesting vitamin A deficiency or excess, or is at risk for vitamin deficiency
Sample Required?
A blood sample taken from a vein in your arm
Test Preparation Needed?
A fasting blood sample is required, and no alcohol should be consumed for 24 hours before sample collection.
The Test Sample
What is being tested?
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 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 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 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.
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?
A fasting blood sample is required and no alcohol should be consumed for 24 hours before sample collection.
The Test
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
- Anaemia
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
- Crohn’s disease
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. Some of the symptoms associated with vitamin A toxicity are:
- Headache
- Nausea and vomiting
- Double or blurred vision
- Fatigue
- Weakness
- Dizziness
- Seizures
- Irritability
- Muscle pain
- Bone and joint pain
- Weight loss
- Hair loss
- Mucous membrane dryness
- Itching
- 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.
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.
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.
Common Questions
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Article Sources
NOTE: This article is based on research that utilizes the sources cited here as well as the collective experience of the Lab Tests Online Editorial Review Board. This article is periodically reviewed by the Editorial Board and may be updated as a result of the review. Any new sources cited will be added to the list and distinguished from the original sources used.
