Allergy testing involves having a skin or blood test to determine what substance, or allergen, may trigger an allergic response in a person. Skin tests are usually done because they are rapid, reliable, and generally less expensive than blood tests, but either type of test may be used.
Skin tests
A small amount of a suspected allergen is placed on or below the skin to see if a reaction develops. There are 3 types of skin tests:
* Skin prick test. This test is done by placing a drop of a solution containing a possible allergen on the skin, and a series of scratches or needle pricks allows the solution to enter the skin. If the skin develops a red, raised itchy area (called a wheal), it usually means that the person is allergic to that allergen. This is called a positive reaction.
* Intradermal test. During this test, a small amount of the allergen solution is injected into the skin. An intradermal allergy test may be done when a substance does not cause a reaction in the skin prick test but is still suspected as an allergen for that person. The intradermal test is more sensitive than the skin prick test but is more often positive in people who do not have symptoms to that allergen (false-positive test results).
* Skin patch test. For a skin patch test, the allergen solution is placed on a pad that is taped to the skin for 24 to 72 hours. This test is used to detect a skin allergy called contact dermatitis.
Blood test
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 not able to have skin tests.
The most common type of blood test is called radioallergosorbent testing (RAST). It is used to measure the blood level of a type of antibody (called immunoglobulin E, or IgE) that the body may produce in response to particular allergens. IgE levels are often higher in people who have allergies or asthma. RAST may be used for people who cannot have skin tests, such as people who take certain medications (such as some antidepressants) that make the results of skin tests less accurate.
Other laboratory testing methods, such as an immunoassay capture test (ImmunoCAP, UniCAP, or Pharmacia CAP), may be used by your health professional to provide additional information.
Skin tests
A small amount of a suspected allergen is placed on or below the skin to see if a reaction develops. There are 3 types of skin tests:
* Skin prick test. This test is done by placing a drop of a solution containing a possible allergen on the skin, and a series of scratches or needle pricks allows the solution to enter the skin. If the skin develops a red, raised itchy area (called a wheal), it usually means that the person is allergic to that allergen. This is called a positive reaction.
* Intradermal test. During this test, a small amount of the allergen solution is injected into the skin. An intradermal allergy test may be done when a substance does not cause a reaction in the skin prick test but is still suspected as an allergen for that person. The intradermal test is more sensitive than the skin prick test but is more often positive in people who do not have symptoms to that allergen (false-positive test results).
* Skin patch test. For a skin patch test, the allergen solution is placed on a pad that is taped to the skin for 24 to 72 hours. This test is used to detect a skin allergy called contact dermatitis.
Blood test
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 not able to have skin tests.
The most common type of blood test is called radioallergosorbent testing (RAST). It is used to measure the blood level of a type of antibody (called immunoglobulin E, or IgE) that the body may produce in response to particular allergens. IgE levels are often higher in people who have allergies or asthma. RAST may be used for people who cannot have skin tests, such as people who take certain medications (such as some antidepressants) that make the results of skin tests less accurate.
Other laboratory testing methods, such as an immunoassay capture test (ImmunoCAP, UniCAP, or Pharmacia CAP), may be used by your health professional to provide additional information.
No comments:
Post a Comment