To determine what a patient is allergic to, a physician will need to perform an allergy test. Allergy tests assess whether a patient has IgE antibodies to a specific allergenic substance. The most commonly performed allergy test is the allergy prick/puncture skin test, in which a small amount of allergen solution is placed on the skin and a tiny sterile needle or plastic device is pricked or punctured through the skin.
After waiting 15 to 20 minutes, the test is read by the physician or the physician’s assistant. A positive test is signified by a small bump, also referred to as a wheal, surrounded by an area of redness, also called the “flare response,” which is usually quite itchy. When physicians are attempting to determine whether a patient with suspected allergic rhinitis has an allergy and what substances should be avoided, a screening test, usually consisting of 10 to 15 allergens, is performed. Alternatively, if an allergy test is being conducted to create a therapeutic vaccine (allergy shots), anywhere from 50 to 70 tests are usually done, depending upon the geographic location where the patient lives. The prick/puncture skin test is highly reliable and accurate, and is considered the gold standard of allergy testing.
If the prick/puncture skin test is negative and allergies are highly suspected, the physician may elect to do additional testing using the intradermal method. This type of test is administered by injecting a small amount of allergen solution into the patient’s skin and again waiting 15 to 20 minutes. A positive test requires the presence of both a wheal and a flare. While a negative intradermal test is very helpful in excluding an allergy to a given substance, a positive intradermal test is not particularly helpful, as many patients who are not actually allergic to a certain allergen may still show positive test results to that substance. For this reason, the intradermal test should only be performed and interpreted by physicians who are highly experienced in diagnosing allergic disease.
Neither the prick nor the intradermal skin test can be performed in patients with diffuse skin disease or those who have taken a medication known to block the allergic response (most commonly antihistamines, such as Benadryl, or tricyclic antidepressants, such as doxepin).
Karen’s comment:
I avoided going to the allergist for many years because I was afraid of having the skin test. I had scratch testing as a child, and it hurt for many hours afterward. My friend convinced me to do it and told me that it wouldn’t be bad. It turned out that the way testing is done now just involves a light pricking of the skin compared with the old method where the skin was actually scraped and scratched. I didn’t have any significant discomfort during the test, and it was not as painful as some blood draws that I’ve had. Prick/puncture skin test Allergy test in which the most superficial layer of skin is pricked or punctured with an allergen extract.
Intradermal test
An allergy test in which an allergen extract is injected into the skin.