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Types of Allergy Tests
Skin Prick
A skin prick test, also known as a scratch test, is a relatively painless procedure that does not involve drawing blood. It is typically conducted on a patient’s back, if they are very young, or on the forearm, where a drop of purified allergen solution is placed on the skin. A small lancet needle is used to prick/scratch the solution into the top layer of the skin; the feeling of a skin prick test is equivalent to a scratch on the skin with a plastic toothpick.
If a patient is allergic to one of the allergens, redness and swelling will appear at the site of the skin prick test within 15 minutes. Skin prick tests are considered to be more reliable, convenient, and less expensive than a blood test for diagnosing an allergy.
Intradermal
An intradermal skin test is slighting different from the skin prick test. Where a skin prick test only scratches the very surface of the skin, an intradermal skin test works under the top layer of skin. To conduct an intradermal skin test, a needle injects a small amount of allergen under the skin of the patient’s forearm. The allergen solution is left to sit for 15-20 minutes. The allergist will read the skin’s reactions to the applied allergens to determine which specific allergen is causing negative effects.
Blood
To use blood tests to diagnose an allergy, a small amount of blood is drawn from a patient’s arm, and sent out to a specialized laboratory to test for the presence of antibodies to specific allergens. Results from a blood test may take a few weeks to receive. An allergist will conduct a blood test to diagnose an allergy under the following conditions:
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A physician advises against the discontinuation of medications that can interfere with test results or cause medical complications
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A patient suffers from severe skin conditions, such as widespread eczema or psoriasis
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A patient has such a high sensitivity level to suspected allergens that any administration of those allergens might result in potentially serious side effects.