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Why would I need this test?
If you have allergy symptoms such as sneezing, itchy eyes, nasal congestion, swelling and wheezing, an allergy test can be done to identify which specific substances (allergens) are triggering your allergic reaction.
Which allergens will I be tested for?
Common allergens include products from dust mites (tiny bugs you can't see), proteins found in pet dander, saliva and urine, molds inside and outside your home, tree, grass and weed pollen, and cockroach droppings. More serious allergic reactions can be caused by venom from insect stings, foods, natural rubber latex or medications.
What types of allergy tests are there?
Allergy testing is usually done by either a skin test - the most common allergy screening - or a blood test.
How are skin tests performed?
A small dose of the suspected allergen is injected just under the skin, or scratched into the skin. When there are several suspected allergens, a "grid" format may be used, so it's clear where each allergen is being placed. The back or the inner forearm may be used for the test, depending on the number of allergens being tested. The allergen extracts or vaccines used in allergy tests are made commercially according to U.S. Food and Drug Administration standards.
What do the results mean?
When you're exposed to an allergen, your body releases a chemical substance or histamine that causes welt-like redness and swelling in the spots where the skin was scratched or pricked. The allergist checks the site to see if there is a local reaction, such as redness, itching or raised bumps. The allergist may also measure the area to see how large the reaction is. A reaction happens quickly within the body, and results are available within 15 minutes of testing.
Could I have a serious reaction to allergens tested?
If the doctor thinks you could have an anaphylactic reaction (dizziness, trouble breathing, and swelling - especially of the face, tongue and throat), that one substance may not even be tested. Or if a patient has an allergic reaction to food or medication, the allergist may do a challenge test.
For this test, the patient inhales or swallows a very small amount of the suspected allergen, such as milk or an antibiotic. If there's no reaction, the dose may be slowly increased. Since challenge tests may cause severe allergic reactions, they're only done when really necessary and must be closely monitored by an allergist.
What is a RAST test?
A RAST (radioallergosorbent test) involves drawing blood. Blood is drawn from a vein and then sent for testing for the presence of allergen-specific antibodies. A RAST test can be done when a skin test can't be done or wouldn't be safe. Both tests are highly specific, but the skin test is cheaper, more sensitive and produces immediate results.
If I test positive for allergies, how will my condition be treated?
There are several ways to treat allergies. Antihistamines are often prescribed to relieve allergy symptoms. Decongestants may help relieve nasal congestion and are often prescribed along with antihistamines. Nasally inhaled corticosteroids that work by reducing the swelling in the membranes of the nose and sinuses are another option.
Allergy shots (desensitization) involve getting injections of small amounts of the triggering allergen. This is similar to vaccinations or immunizations. That is, your body will react to the injected allergen by building immunity to it. Subsequent environmental exposures to this allergen will not be as likely to trigger an allergic response.
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External Sources
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The American Academy of Allergy, Asthma and Immunology
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The Merck Manual of Medical Information.
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This article was reviewed and updated June 2007.
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