This is a test to measure the amount of vitamin A (see also beta-carotene) in the blood.

Adult or child:

Blood is drawn from a vein, usually from the inside of the elbow or the back of the hand. The puncture site is cleaned with antiseptic, and an elastic band is placed around the upper arm to apply pressure and restrict blood flow through the vein. This causes veins below the band to fill with blood.

A needle is inserted into the vein, and the blood is collected in an air-tight vial or a syringe. The band is then removed to restore circulation. After blood has been collected the needle is removed, and the puncture site is covered to stop any bleeding.

For an infant or young child, the area is cleansed with antiseptic and punctured with a sharp needle or a lancet. The blood may be collected in a pipette (small glass tube), on a slide, onto a test strip, or into a small container. A bandage may be applied to the puncture site if there is any bleeding.

Fast 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.

To investigate the possibility of vitamin A deficiency or excess, both of which are rare in the developed world.

Normal values range from 50 to 200 mcg/dl. Normal value ranges may vary slightly among different laboratories.

Abnormal values reflect a deficiency of vitamin A that may be associated with:

• Developmental aberrations of bones or teeth in young children
• Dry or inflamed eyes
• Hair loss
• Loss of appetite
• Malabsorption syndrome (for example, celiac disease, sprue)
• Night blindness
• recurring infections
• Skin rashes
• Steatorrhea (fat malabsorption -- inadequate absorption of fats from the intestinal tract)

Risks associated with venipuncture are slight:

• Excessive bleeding
• Fainting or feeling lightheaded
• Hematoma (blood accumulating under the skin)
• Infection (a slight risk any time the skin is broken)
• Multiple punctures to locate veins

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.