Vitamin A is a fat-soluble vitamin. This article describes the test used to measure the amount of vitamin A in the blood.

See also: Beta-carotene test

Retinol test

A blood sample is needed. For information on how this is done, see: Venipuncture

Do not eat or drink anything for 4 hours before the test.

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.

This test is done to determine if you have too much or too little vitamin A in your blood. However, such conditions are uncommon in the United States.

Normal values range from 50 to 200 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.

Lower than normal values mean you do not have enough vitamin A in your blood. This may cause:

• Bone or teeth problems in young children
• Dry or inflamed eyes
• Hair loss
• Loss of appetite
• Night blindness
• Recurring infections
• Skin rashes

A vitamin A deficiency may occur if your body has trouble absorbing fats through the digestive tract. This may occur if you have:

• Celiac disease
• Cystic fibrosis
• Pancreatitis

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 lightheaded
• Hematoma (blood accumulating under the skin)
• Infection (a slight risk any time the skin is broken)

Mason JB. Vitamins, trace minerals, and other micronutrients. In: Goldman L, Schafer AI, eds. Cecil Medicine. 24th ed. Philadelphia, PA: Saunders Elsevier; 2011:chap 225.