A blood sample is needed.

Follow your health care provider's instructions about not eating or drinking anything for up to 24 hours before the test.

When the needle is inserted to draw blood, some people feel moderate pain. Others feel only a prick or stinging. Afterwards, there may be some throbbing or slight bruising. This soon goes away.

This test is done to check if you have too much or too little vitamin A in your blood. (These conditions are uncommon in the United States.)

Normal values range from 20 to 60 micrograms per deciliter (mcg/dL) or 0.69 to 2.09 micromoles per liter (micromol/L).

Normal value ranges may vary slightly among different laboratories. Some labs use different measurements or test different samples. Talk to your provider about the meaning of your specific test results.

A lower than normal value means you do not have enough vitamin A in your blood. This may cause:

• Bones or teeth that do not develop correctly
• Dry or inflamed eyes
• Feeling more irritable
• Hair loss
• Loss of appetite
• Night blindness
• Recurring infections
• Skin rashes

A higher than normal value means you have excess vitamin A in your blood (toxic levels). This may cause:

• Anemia
• Bone and muscle pain
• Diarrhea
• Double vision
• Hair loss
• Increased pressure in the brain (pseudotumor cerebri)
• Lack of muscle coordination (ataxia)
• Liver and spleen enlargement
• Loss of appetite
• Nausea

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

• Chronic lung disease called cystic fibrosis
• Pancreas problems, such as swelling and inflammation (pancreatitis) or the organ not producing enough enzymes (pancreatic insufficiency)
• Small intestine disorders that reduce nutrient absorption, such as celiac disease

There is little risk involved with having your blood taken. Veins and arteries vary in size from one person to another and from one side of the body to the other. Taking blood 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)
• Multiple punctures to locate veins

Retinol test

Markell M, Siddiqui HA. Vitamins and trace elements. In: McPherson RA, Pincus MR, eds. Henry's Clinical Diagnosis and Management by Laboratory Methods. 24th ed. Philadelphia, PA: Elsevier; 2022:chap 27.

Ross AC. Vitamin A deficiencies and excess. In: Kliegman RM, St. Geme JW, Blum NJ, Shah SS, Tasker RC, Wilson KM, eds. Nelson Textbook of Pediatrics. 21st ed. Philadelphia, PA: Elsevier; 2020:chap 61.

Updated by: Jacob Berman, MD, MPH, Clinical Assistant Professor of Medicine, Division of General Internal Medicine, University of Washington School of Medicine, Seattle, WA. Also reviewed by David C. Dugdale, MD, Medical Director, Brenda Conaway, Editorial Director, and the A.D.A.M. Editorial team.