What is allergy testing?
If you have a stuffy nose, trouble breathing (especially in the summer), or hives after eating certain foods, you may have an allergy. Allergy tests can help you and your doctor find out if these problems are caused by an allergy and which things you are allergic to. That way you can stay away from the things that trigger your allergic reaction.
What kinds of allergy tests are available?
There are several types of specific allergy tests.
- Skin test
- Blood tests
- Immediate-type hypersensitivity (IgE) skin tests are typically used to test for airborne allergens, foods, insect stings, and penicillin. Immediate-type hypersensitivity also can be evaluated through serum IgE antibody testing called radioallergosorbent testing (RAST).
- Delayed-type hypersensitivity skin tests (patch-type skin tests) are commonly used in patients with suspected contact dermatitis. Some common allergens for patch testing are rubber, medications, fragrances, vehicles or preservatives, hair dyes, metals, and resins.
About 15 minutes after the application tothe skin, the test site is examined for a wheal and flare reaction. A positive skin test reaction (typically, a wheal of 3 mm or greater in diameter than the negative control reaction, accompanied by surrounding erythema) reflects the presence of mast cellAboundIgE specific to the tested allergen.
Skin tests are very common – There are three main kinds of skin tests.
- Scratch or a Prick Test – The first kind is called a “Scratch” or a “prick” test. Positive-control skin tests (histamine) and negative-control skin tests (diluents) are essential for correct interpretation of skin test reactions. A tiny drop of testing allergen fluid is placed on your skin. Then, the skin is pricked through the drop. After 15 minutes, the test site is checked for redness and swelling. There’s a “prick” sensation when the testing is applied, but it doesn’t hurt a lot. Usually, about 240 prick tests are needed for a full exam.
- Intra-dermal Tests: In the second kind of skin test, the testing fluid is injected into your skin (like a shot). This test is used to check for allergy to medicines (most often penicillin) and bee-sting allergy.
- Patch Test– A small patch of material soaked in testing fluid is taped on your skin. After 2 or 3 days, your doctor will take off the patch and look for redness and swelling in your skin. Patch tests are used to evaluate rashes caused by allergy to things that might rub against your skin.
Some commonly used medicines, like pain killers and antihistamines, can interfere with skin tests. If you take these medicines, you have to stop taking them before skin tests can be done.
Why should I be tested for allergies?
It is not always necessary to have allergy tests. In some cases, it can be easier to skip the tests and go straight to taking allergy medicines. There are a number of safe and effective medicines that work well for most allergies. If these medicines do not work for you, or if you have severe allergy reactions, allergy testing may be helpful.Allergy tests can help you find out what you are allergic to. Once you know what you are allergic to, you can try to stay away from it. Having established a correct allergy diagnosis, the physician is better equipped to select appropriate therapeutic interventions for that patient, such as allergen avoidance, medications, and, sometimes, immunotherapy. For example, a patient with a specific pollen allergy may be instructed to increase medication use during the pollen season. Patients with an animal allergy may be instructed to use allergy or asthma medication before exposure. After specific testing, avoidance measures can be targeted to allergens to which the patient is known to be allergic.
