While a tentative diagnosis of allergic disease can often be made from a patient’s clinical history, many allergic conditions exhibit symptoms that are hard to distinguish from nonallergic conditions. The American Academy of Allergy, Asthma and Immunology recommends the use of objective measures to confirm the diagnosis of allergy in symptomatic patients. Skin testing or in vitro assays of IgE to specific allergens are particularly recommended when:
- Patients present with persistent symptoms that can be associated with specific allergens;
- The condition adversely affects the patients quality of life; and
- Immunotherapy (allergy shots) is contemplated.
Diagnostic testing of the potentially allergic patient serves a number of important purposes including:
- Confirming the diagnosis of the allergy;
- Differentiating allergic disease from other disorders;
- Identifying the offending allergen; and
- Guiding the development of appropriate treatment or allergen avoidance plans.
The most traditionally used diagnostic allergy tests in the United States are skin tests using extracts of specific allergens.
A number of different skin testing techniques are used. The three most commonly used methods are prick, puncture and intradermal. Both skin testing and in vitro allergen-specific IgE testing employ carefully prepared extracts of allergens or, in some cases, liquid allergens themselves.
For prick and puncture testing, a small drop of allergen is places on the skin. In prick testing, a sharp needle is introduced into the skin at an angle and used to lift up the outer layers of skin slightly. This allows the extract to penetrate the skin. In puncture testing, a small lancet or bifurcated needle is introduced at a perpendicular angle to the skin to produce a small puncture, allowing extract to enter. Intradermal skin testing involves the use of a tuberculin syringe and small gauge needle to inject a small amount of diluted extract under the skin.
Skin testing by any of the methods above is highly technique-dependent, and should only be performed by specialist who is trained in proper procedures and interpretation of results.
It is also important that any office performing skin testing have staff available who are able to handle the potentially life-threatening reactions that can rarely occur with the administration of these tests.