An allergy scratch test is a diagnostic procedure to determine if an individual exhibits an allergic reaction to common allergens. It allows testing without risking a severe allergic reaction.
The patient is scratched with a needle to break the upper layer of the skin. At that point, a solution containing a diluted concentration of the allergen is introduced to the scratch. Another way to perform the test is to break the skin with a circular tool that leaves a small blister and to use a needle and syringe to introduce the allergen into the space under the blister. After about half-an-hour, the samples are examined. In patients with no allergic reaction, there is no discernible change to the site, but where an allergy exists, the area shows redness from inflammation and often an increased clotting response.