Why the test Is performed?

Allergy tests are used to determine the specific substances that cause an allergic reaction in an individual. They may also be used to determine if a group of symptoms is a true allergic reaction (involving antibodies and histamine release). 

How to perform the test?

There are many methods of allergy testing. Among the more common are the skin tests, elimination-type tests, and the radioallergosorbent test (RAST).

Skin tests are the most common. Specific methods vary. The scratch test (one of the most common methods) involves placement of a small amount of suspected allergy-causing substances on the skin, and then scratching or pricking the skin so that the allergen is introduced under the skin surface. The skin is observed closely for signs of a reaction, usually swelling and redness of the site. Results are usually obtained within about 20 minutes, and several suspected allergens can be tested at the same time. Skin tests are most useful for respiratory allergies , a penicillin allergy, and insect bite allergies.

Food allergies are usually tested by using various "elimination" diets (in which the suspected food(s) are eliminated from the diet for several weeks and then gradually re-introduced one at a time while the person is observed for signs of an allergic reaction). Because food allergies are often affected by what the person thinks they might be allergic to, a double-blind test may be advised.

The RAST is a laboratory test performed on blood (see venipuncture). It tests for the amount of specific IgE antibodies in the blood (which are present if there is a "true" allergic reaction). 

Preparation for the test

Before any allergy testing, the health care provider will ask for a very detailed medical history. This may include questions about such things as illnesses, emotional and social conditions, work, entertainment, lifestyle, foods, and eating habits. 

Abnormal results`s meaning

Most often, a positive test indicates an allergy to the substance in question. The skin tests are most reliable when testing for airborne substances (such as animal dander or pollen). However, if the dose of allergen is excessive, a positive reaction will occur even in persons who are not allergic.

The risks of the test

Skin tests and food allergy tests carry a risk that you will experience an allergic reaction when exposed to the allergens. Some sensitive persons will (rarely) experience a life-threatening anaphylactic reaction.

Penicillin are the only drugs that can be tested using skin tests. (Skin tests for other drugs are at best non-informative and can be dangerous).

Tests that are not proven as valid include cytotoxic testing (in which foods are mixed in a test tube with a sample of the person's blood and then the white blood cells are observed for a change in shape) and "provocation and neutralization" testing (in which the person is injected with a food or other substance and, if there is an allergic reaction, they are injected with more of the substance to "neutralize" the response; this can be very dangerous!)