Common Allergy Testing Procedures

An allergy test of one form or another is often needed to determine which substance is causing the adverse reaction, especially if the problem seems to be originating from a food allergy. Testing may reveal that the individual is not allergic to the suspect food but rather to an ingredient in the food. Peanut oil, for instance, is a common culprit.

Although there are many allergy testing methods used to determine the presence of allergens, but the three most common allergy testing procedures are skin tests, elimination tests, and the radioallergosorbent test (RAST). It should be noted, however, that the accuracy of these tests varies widely and even the same test performed at different times may yield different results. It is also possible for a person to react to a substance during testing but not under normal exposure. False negatives occur often.

SKIN TESTS

Allergy skin testing is by far the most used of the three methods but it too varies in methodology. With the scratch test a small amount of the suspected allergen is placed on the forearm or upper arm (or on the back) and then introduced under the surface by scratching or pricking. The skin is then observed for swelling or redness. Results normally appear in about 20 minutes and the test can be conducted with a number of suspected allergens at one time. Skin tests are useful in detecting respiratory allergies, penicillin allergy, insect allergies, and food based allergies.

ELIMINATION TESTS

Food allergies are also often investigated via an elimination diet. Suspect foods are removed from the diet for several weeks and then re-introduced one at a time with the person monitoring their reactions. Because some people become convinced that they are allergic to a given food, double blind tests are sometimes required in which suspect foods and harmless placebos are disguised and given to the patient.

RADIOALLERGOSORBENT TEST (RAST)

Food allergies can be extremely severe however and given the potential for a life-threatening reaction, an allergy blood test is often a safer approach. The radioallergosorbent or RAST test is performed in a laboratory and tests for specific amounts of IgE antibodies that will be present in the blood during a true allergic reaction.

Continue to: How to Prepare for Allergy Test

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