When combined with detailed medical history, an allergy test can identify the specific things that trigger your allergic reaction. The following tests are commonly used to test for allergies in adults. Allergy tests include skin tests or blood tests to find out what substance or allergen can trigger an allergic reaction in a person. Skin testing is usually done because it is faster, effective, and generally cheaper than blood tests, but both types of tests can be used.
The following types of allergy tests:
A small number of suspected allergens are placed on or under the skin to see if the reaction develops. There are three types of skin tests:
• Skin prick test. This test is done by placing a drop of a solution containing allergens on the skin, and a series of scratches or needle stabs to insert the solution into the skin. If the skin builds a region, itchy red lifting (called wheal), usually means that the person is allergic to the allergen. This is called a positive reaction.
• Intradermal test. During this test, a small amount of allergen solution is injected into the skin. An intradermal allergy test may be performed if the substance does not cause a reaction in the skin prick test, but is still suspected of causing the allergy to the person. Intradermal tests are more sensitive than skin prick test, but are more often positive in people who have no symptoms with allergens (false positive test results).
• Skin patch test. For skin patch test, the allergen solution is placed on a pad attached to the skin for 24 to 72 hours. This test is used to detect skin allergies called contact dermatitis.
Allergy blood tests look for substances in the blood called antibodies. Blood tests are not as sensitive as skin tests, but are often used for people who are unable to perform skin tests. The most common type of blood test used is the enzyme-linked immunosorbent (ELISA, AMDAL) test. IgE levels are often higher in people who have allergies or asthma. Other laboratory testing methods, such as radioallergosorbent testing (RAST) or catching immunoassay tests (ImmunoCAP, UniCAP, or Pharmacia CAP) may be used to provide more information.
An allergy blood test is often used because:
• Patients consume drugs that may interfere with skin tests, but can not be stopped for several days
• Patients suffer from a severe skin condition such as eczema or psoriasis
Tests with strong allergens may cause extra-large positive reactions
• For very young infants and children, a single syringe for a blood allergy test may be better than some skin tests