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Allergy testing involves having a skin or blood test to find out 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.
A small amount of a suspected allergen is placed on or below the skin to see if a reaction develops. There are three types of skin tests:
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 used is the enzyme-linked immunosorbent assay (ELISA, EIA). It measures the blood level of a type of antibody (called immunoglobulin E, or IgE) that the body may make in response to certain allergens. IgE levels are often higher in people who have allergies or asthma.
Other lab testing methods, such as radioallergosorbent testing (RAST) or an immunoassay capture test (ImmunoCAP, UniCAP, or Pharmacia CAP), may be used to provide more information.
Your allergy test results may show that allergy treatment is a choice for you.
Food-specific immunoglobulin G (IgG) antibody testing measures the level of a type of antibody (called food-specific IgG antibodies) in the blood. IgG antibody tests are not recommended to find out whether a person has a food allergy. There is no evidence that food-specific IgG antibodies show a food allergy or sensitivity. It is normal for people to have IgG antibodies to foods that they tolerate.
Allergy testing is done to find out what substances (allergens) may cause an allergic reaction.
The skin test can be done to:
A blood test may be done instead of a skin test if a person:
Be sure to tell your doctor about all the medicines you take. You may need to stop taking some medicines such as antihistamines for a few days before you have an allergy skin test.
The health professional doing the skin prick or intradermal test will:
Another skin prick method uses a device with 5 to 10 points (heads), which are dipped into bottles that contain the allergen extract. This device is pressed against the skin of the forearm or back so that all heads are pressed into the skin at the same time.
A skin patch test also uses small doses of the suspected allergen. For this test:
Allergy skin tests usually take less than an hour.
A health professional uses a needle to take a blood sample, usually from the arm.
The blood sample will be placed on specially treated paper. It's then sent to a lab to find out if antibodies to any of the allergens being tested are present. If specific antibodies are found, it may mean you are allergic to a certain allergen.
With the skin prick test and the intradermal skin test, you may feel a slight pricking sensation when the skin beneath each sample is pricked or when the needle penetrates your skin.
You may feel nothing at all from the needle, or you may feel a quick sting or pinch.
The major risk with the skin prick test or the intradermal skin test is a severe allergic reaction called anaphylaxis. Symptoms of this type of reaction include itching, wheezing, swelling of the face or entire body, trouble breathing, nausea, vomiting, and low blood pressure that can lead to shock. An anaphylactic reaction can be life-threatening and is a medical emergency. Emergency care is always needed for this type of reaction. But severe allergic reaction is rare, especially with the skin prick test.
There is very little chance of having a problem from this test. A small bruise may form at the site.
No raised red areas (called wheals) are created by the allergen.
A wheal created by the allergen is at least 3 mm (1/8 inch) larger than the reaction to the negative control. The larger the wheal, the more certain it is that the person is allergic to that specific allergen.
The levels of immunoglobulin E (IgE), a type of antibody, are the same as in a person who does not have allergies.
The levels of immunoglobulin E (IgE) antibodies for a particular allergen or group of allergens are above the normal level.
Adaptation Date: 11/16/2021
Adapted By: Alberta Health Services
Adaptation Reviewed By: Alberta Health Services
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