Vitamin A

Also Known As

Retinol

Formal Name

Retinol

This article was last reviewed on

12 June 2023.

This article waslast modified on 12 June 2023.

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 of vitamin deficiency such as patients on nutrition supplements.

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.

On average it takes 7 working days for the blood test results to come back from the hospital, depending on the exact tests requested. Some specialist test results may take longer, if samples have to be sent to a reference (specialist) laboratory. The X-ray & scan results may take longer. If you are registered to use the online services of your local practice, you may be able to access your results online. Your GP practice will be able to provide specific details.

If the doctor wants to see you about the result(s), you will be offered an appointment. If you are concerned about your test results, you will need to arrange an appointment with your doctor so that all relevant information including age, ethnicity, health history, signs and symptoms, laboratory and other procedures (radiology, endoscopy, etc.), can be considered.

Lab Tests Online-UK is an educational website designed to provide patients and carers with information on laboratory tests used in medical care. We are not a laboratory and are unable to comment on an individual's health and treatment.

Reference ranges are dependent on many factors, including patient age, sex, sample population, and test method, and numeric test results can have different meanings in different laboratories.

For these reasons, you will not find reference ranges for the majority of tests described on this web site. The lab report containing your test results should include the relevant reference range for your test(s). Please consult your doctor or the laboratory that performed the test(s) to obtain the reference range if you do not have the lab report.

For more information on reference ranges, please read Reference Ranges and What They Mean.

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 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.

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