What is allergy testing?
Allergy testing is the preliminary step for physicians to determine whether a patient has allergic reactions to a variety of common allergens after being exposed to them during a series of tests. Depending on the results of allergy testing, allergists may decide to put patients to undergo a regular allergy shot regimen, begin an allergy medication regimen or practice a variety of behavioral modification techniques to reduce the likelihood of allergic reactions.
Skin tests are the primary means of testing a patient for allergic reactions, but these can take on a variety of different forms. The most common allergy testing methods include:
Skin Prick Test
A skin prick test, also known as a puncture or scratch test, which involves testing the allergic reactions of more than 40 different substances at once, such as dust mites, pollen, mold, pet dander and common foods. These tests are done on the patient's forearm, while children may be tested on the lower back. These tests are relatively painless and use a small needle or lancet that barely penetrate the skin's surface.
In addition to directly exposing the skin to allergens, allergists will begin by applying small amounts of histamine or saline to the skin. If the body reacts to saline, it could mean that the skin is overly sensitive, while if a person's body does not react to histamine, it may not be able to reveal an allergy even if a person has one. After about 15 minutes, the allergist will examine the test area to search for red, itchy bumps that signal an allergic reaction to each individual substance.
Skin Injection Test
For specific types of allergens, a skin prick test is not enough to check for the presence of an early reaction, so allergists may choose to perform a skin injection test, or intradermal test, instead. This involves injecting a small amount of an allergen extract right under the skin of the patient, which is examined after 15 minutes for signs of an allergic reaction. Much like a skin prick test, this will manifest itself as an itchy, red bump on the skin. This test is only done for specific types of allergens, such as penicillin or insect venom.
This form of testing is ideal for contact dermatitis, or skin reactions when exposed to an allergen. Instead of using needles, patients will wear a patch with up to 20 to 30 different allergenic extracts that will test for delayed allergic reactions, which can take several days to surface. These patches are worn on the arm or back for 48 hours and removed/inspected upon returning to the doctor's office. Patch testing typically tests less common allergens such as metals, dyes, latex, fragrances, preservatives and more.