Allergy TestingEn Español (Spanish Version)
Allergy tests are used to determine which substances cause allergic reactions. Two types of tests can be used to confirm an allergy diagnosis:
Blood tests—a small sample of blood is taken and tested for dozens of different allergens. Also called RAST testing or in vitro testing.
Skin tests—applying suspected allergens to the skin to see if they elicit an allergic reaction (raised or irritated skin). Also called scratch testing or skin-prick testing.
Parts of the Body Involved
Skin testing is usually done on the forearm or upper back. For blood testing, blood is drawn from a vein in the arm.
Reasons for Procedure
Allergy tests are used to determine which substances cause an allergic reactions. Once allergic triggers are identified, a person can take the steps to avoid or lessen contact with the substance. This will reduce the chance of allergic reactions. Individuals can also receive allergy shots to reduce their reaction to the allergens.
What to Expect
Prior to Procedure
Keep a diary of your allergy symptoms. When you experience symptoms, write down the time of day, where you are, what you ate, and what you have come in contact with that could trigger the allergic reaction. Make sure to bring the diary with you to your doctor's appointment.
A blood sample will be taken from a vein in your arm or suspected allergens will be applied to your skin.
Anesthesia is not needed for allergy testing.
Description of the Procedure
Medications with antihistamine properties and oral steroids can decrease allergic reactions. Ask your doctor when to discontinue them before the skin testing.
Blood testing—A sample of blood will be drawn from your arm. To do this, you will roll up your sleeve and the nurse or lab technician will tie a tourniquet around your upper arm. A needle will be inserted into a vein in your arm and a small amount of blood will be drawn into a vial. The blood sample will be sent to a laboratory where it will be tested to determine what substances you are allergic to.
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Skin testing—The suspected allergen is applied directly to the skin, usually on the forearm or back. The substance is either applied to a shallow scratch made on the skin or a skin-prick needle pushes the substance into the surface layer of the skin. For every allergen tested, you will have a separate scratch or skin prick. If you are allergic to one of the test substances, redness and swelling will appear at the site usually within 15-20 minutes.
There are usually no special instructions or restrictions after allergy testing.
How Long Will It Take?
Blood testing—Drawing the blood takes approximately 3 minutes. Laboratory result time varies depending on the laboratory. Results are generally be available within a few days or a week.
Skin testing—If you are allergic, a reaction will usually develop in about 15-20 minutes.
Will It Hurt?
There may be mild irritation where the substance is applied to the skin.
Allergy testing carries minimal risk. Occasionally a skin test can result in a significant area of redness and irritation.
Blood testing—A small bruise or collection of blood under the skin may develop at the site of the needle stick.
Skin testing—There may be some mild irritation at the test site.
Average Hospital Stay
None. This test is performed in your doctor's office or in a clinic or hospital laboratory.
Once specific allergens have been identified, steps can be taken to avoid these triggers and lessen allergic symptoms. Ask your doctor to give you detailed information on ways to take control of your allergies. Adjust your activities to avoid exposure to allergens that bother you. Once you are diagnosed, pay close attention to possible triggers and discuss these with your doctor.
American Academy of Allergy, Asthma, and Immunology
National Institute of Allergy and Infectious Diseases, National Institutes of Health
Allergy Asthma Information Association
Calgary Allergy Network
American Academy of Allergy, Asthma, and Immunology website. Available at: http://www.aaaai.org .
Behrman RE, Kliegman RM, Jenson HB, eds. Nelson Textbook of Pediatrics . 17th Edition. Saunders: Philadelphia, PA; 2004.
Journal of the American Medical Association . Asthma Information Center.
Sheikh J. Rhinitis, allergic. Emedicine website. Available at: www.emedicine.com/med/topic104.htm. 2005.
Last reviewed March 2008 by Elie Rebeiz, MD, FACS
Please be aware that this information is provided to supplement the care provided by your physician. It is neither intended nor implied to be a substitute for professional medical advice. CALL YOUR HEALTHCARE PROVIDER IMMEDIATELY IF YOU THINK YOU MAY HAVE A MEDICAL EMERGENCY. Always seek the advice of your physician or other qualified health provider prior to starting any new treatment or with any questions you may have regarding a medical condition.
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