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 4 hours before the test.
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
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.
What abnormal results mean
Lower than normal values mean you do not have enough vitamin A in your blood. This may cause:
David C. Dugdale, III, MD, Professor of Medicine, Division of General Medicine, Department of Medicine, University of Washington School of Medicine. Also reviewed by David Zieve, MD, MHA, Medical Director, A.D.A.M., Inc.