Allergy testing

Allergy testing encompasses a variety of tests to detect an allergic response, that is, immune system overreaction to something inhaled, ingested or touched. This may include skin, blood or challenge testing, the latter necessitating close supervising by a specialized physician, typically an allergist.

Skin test
Skin testing for allergies can come in a variety of forms: a skin prick test, also called a puncture or scratch test; a skin injection test; or a patch test.

Skin prick test
Skin prick testing tests for allergic reactions to as many as 40 different substances by lightly pricking the skin with the potential allergens, using a new lancet for each substance. These scratches are superficial and only briefly uncomfortable; they do not draw blood. The test compares the skin's reaction to these substances to two controls: histamine and either glycerin or saline. Histamine typically prompts a skin reaction; if it does not, the rest of the testing may produce false negatives. On the other hand, most people will not react to either glycerin or saline. If you do, this skin sensitivity make cause false positives in the rest of your testing and any positive results will be interpreted cautiously.

Results take about 15 minutes and an allergic reaction indicated by a raised, red, itchy bump (wheal) at the site, which the provider performing the test will measure.

At-home testing
The Cleveland Clinic cautions against at-home testing, citing potential errors and misinterpretation that doctor-supervised testing can help avoid, like mistaking as an allergy what is actually an intolerance or an infection. For instance, at-home tests may evaluate for immunoglobulin G (IgG) instead of immunoglobulin E (IgE), but only the latter indicates allergy. Hair follicles, used by some at-home kits in lieu of blood sample, contain no IgE so cannot confirm an allergy.