A blood sample is needed. For information on how this is done, see: Venipuncture
How to prepare for the test
Do not eat or drink anything for 6 hours before the test. Your health care provider may also tell you to temporarily stop taking drugs, such as retinol, that may interfere with test results.
How the test will feel
When the needle is inserted to draw blood, some people feel moderate pain, while others feel only a prick or stinging sensation. Afterward, there may be some throbbing.
Why the test is performed
Your health care provider may order this test if you have signs that your vitamin A level may be too low, such as:
Bones or teeth that do not develop correctly
Dry or inflamed eyes
Feeling more irritable
Loss of appetite
Problems seeing at night
The test can also be used to help measure how well your body absorbs fats.
The normal range is 50 to 300 micrograms per deciliter.
The examples above are common measurements for results of these tests. Normal value ranges may vary slightly among different laboratories. Some labs use different measurements or test different samples. Talk to your doctor about the meaning of your specific test results.
Your intestines are not able to absorb fats very well. Beta-carotene is absorbed along with fats, so it will not be absorbed unless fats are too.
Your diet does not have enough beta-carotene
While this test is a valuable part of the diagnosis of vitamin A deficiency, the test results must be evaluated along with other clinical findings.
What the risks are
Veins and arteries vary in size from one patient to another and from one side of the body to the other. Obtaining a blood sample from some people may be more difficult than from others.
Other risks associated with having blood drawn are slight but may include:
Fainting or feeling light-headed
Hematoma (blood accumulating under the skin)
Infection (a slight risk any time the skin is broken)
Fischbach FT, ed. Manual of Laboratory & Diagnostic Tests. 7th ed. Philadelphia, Pa: Lippincott Williams & Wilkins; 2004.
Lewis JH. Liver disease caused by anesthetics, toxins, and herbal preparations. In: Feldman M, Friedman LS, Brandt LJ, eds. Sleisenger & Fordtran’s Gastrointestinal and Liver Disease. 9th ed. Philadelphia, Pa: Saunders Elsevier; 2010:chap 87.
Linda J. Vorvick, MD, Medical Director, MEDEX Northwest Division of Physician Assistant Studies, University of Washington, School of Medicine. Also reviewed by David Zieve, MD, MHA, Medical Director, A.D.A.M., Inc.