Beta-carotene is the precursor to vitamin A. A test can be done to measures the amount of beta-carotene in blood.
See also: Vitamin A test
How the test is performed
Blood is drawn from a vein, usually from the inside of the elbow or the back of the hand. The site is cleaned with germ-killing medicine (antiseptic). The health care provider wraps an elastic band around the upper arm to apply pressure to the area and make the vein swell with blood.
Next, the health care provider gently inserts a needle into the vein. The blood collects into an airtight vial or tube attached to the needle. The elastic band is removed from your arm.
Once the blood has been collected, the needle is removed, and the puncture site is covered to stop any bleeding.
In infants or young children, a sharp tool called a lancet may be used to puncture the skin and make it bleed. The blood collects into a small glass tube called a pipette, or onto a slide or test strip. A bandage may be placed over the area if there is any bleeding.
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 doctor may order this test if you have signs of a vitamin A deficiency. Beta-carotene breaks down to become vitamin A in the body.
The test can also be used as an indirect way to measure how your body absorbs fats. Beta-carotene is a fat-soluble nutrient. That means it is stored in the body's fatty tissue
The normal range is 50 to 300 micrograms per deciliter.
Note: Normal value ranges may vary slightly among different laboratories. Talk to your doctor about the meaning of your specific test results.
What abnormal results mean
Increased levels may be due to:
Lower than normal levels may be due to:
- A problem with intestinal absorption of fat-soluble substances
- A diet inadequate in beta-carotene, leading to vitamin A deficiency
Signs of vitamin A deficiency include:
- Bone or teeth development problems
- Dry or inflamed eyes
- Hair loss
- Loss of appetite
- Recurring infections
- Skin rashes
- Unexplained irritability
- Vision problems (inability to see at night)
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:
- Excessive bleeding
- 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. 8th ed. Philadelphia, Pa: Saunders Elsevier; 2006:chap 84.
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.
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