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Testing options

Family background, personal history and a physical examination will help your physician determine if an allergy is likely. If your doctor suspects allergy, only an allergy test can tell for sure. Steps can then be taken to identify the specific allergens triggering your symptoms. Four types of tests can be used to confirm an initial allergy diagnosis. While any of these tests can give you answers, they do differ in regard to comfort and convenience.

Blood testing is done in a laboratory and is referred to as in vitro (in glass) testing or IgE blood testing. Measuring the amount of IgE in one blood sample can determine if you are allergic, and exactly what you are allergic to. You can be tested for dozens of different allergens at the same time and from just one blood sample. The simple blood draw can be done at your family doctor’s office.

The ImmunoCAP® Allergy blood test is the latest technology in allergy testing. ImmunoCAP is cleared by the Food and Drug Administration (FDA) and is endorsed by the National Institutes of Health (NIH) and other health organizations. Leading institutions such as Johns Hopkins, the Mayo Clinic and the Cleveland Clinic use ImmunoCAP for their patients. To find a testing location near you, use the pull-down menu on the left.

Skin testing is done by applying suspected allergens directly to the skin (usually on the forearm or back) with a skin-prick device or needle. That means one prick or poke for each and every allergen for which you're being tested. The appearance of a raised welt or other irritation means you're sensitive to the test, but it doesn't always mean you're allergic. Skin testing carries a risk of reaction, because the process requires that allergy triggers be injected directly under the skin. Skin testing is performed routinely by allergists.

Food challenge is a double-blind test used to diagnose food allergy. Various foods, some of which are suspected of inducing an allergic reaction, are placed in individual capsules. The patient is asked to swallow a capsule and is then observed to see if there is a reaction. This process is repeated until all the capsules have been swallowed. In a true double-blind test, the doctor is also "blinded" (the capsules are prepared by another medical professional) so that neither the patient nor the doctor knows which capsule contains the allergen.(1)

The advantage of a food challenge is that if the patient has a reaction only to suspected foods and not to others, it confirms the diagnosis. Someone with a history of severe reactions, however, cannot be tested this way. This type of testing is most commonly used when the doctor believes the reaction a person is describing is not due to a specific food, and the doctor wishes to obtain evidence to support this judgment so that additional efforts may be directed at finding the real cause of the reaction.(1)

Patch or epicutaneous testing is used to determine what’s causing contact eczematous dermatitis. Before administering this test, the patient’s hobbies, habits, occupation and use of cosmetics, lotions, cleansers and ointments are considered. Consultation with an allergist and/or dermatologist is also recommended. A patch containing the suspected allergens is applied to the upper back or arm, depending on the number of possible allergens, and remains on for 48 hours. The skin is then examined for allergic reactions.

1) Fact Sheet: Food Allergy and Intolerances. Bethesda, MD: Office of Communications and Public Liaison. National Institute of Allergy and Infectious Diseases. National Institutes of Health. Public Health Service. U.S. Department of Health and Human Services. June 2001.