Diagnostic Tests for Allergies

These tests will help you and your healthcare provider or allergist know what substances cause your allergy symptoms. Diagnostic tests for allergies may include:

• Skin tests. These are the most common allergy tests. Skin tests measure if you have IgE antibodies to certain allergens such as foods, pollens, or animal dander. A small amount of allergen is put on the skin. The area is then pricked or scratched. If you are allergic to the allergen, a small raised bump like a mosquito bite appears after about 15 minutes. Testing for many allergens may be done at the same time. An allergist may also do an intradermal test. In this test, you are given a shot (injection) of a small amount of allergen just under the skin. This type of skin testing is more sensitive than prick or scratch testing. Skin test results are available right after the testing is done.

• Blood tests. Blood tests for allergies measure IgE antibodies to certain allergens in the blood. The testing that is most often used is called RAST (radioallergosorbent test). Or you may have a newer blood test called an ELISA (enzyme-linked immunosorbent assay). Blood tests may be used when skin tests can't be done. For instance, you may have a blood test if you have certain skin conditions or a very recent severe allergic reaction. A positive blood test does not always mean that you have a specific allergy. These tests take longer to get results and may cost more than skin testing.

• Challenge test. This test is always supervised by an allergist. You eat or breathe in (inhale) a very small amount of an allergen. Then you are closely watched for an allergic reaction. Challenge testing is often done to test for food or medicine allergies when an allergist thinks you have a low risk for reaction. Don't try this at home.

Your healthcare provider will talk with you about the test results. They know your health history and will be able to advise the best way to manage or treat your allergy.