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How Do Doctors Test for Food Allergies?

How do doctors test for food allergies?
Deborah

Doctors often use a combination of skin testing and blood testing to diagnose a food allergy.

One common skin test is a scratch test. An allergy doctor (allergist) or nurse puts a tiny bit of an allergen (such as a liquid with a very small amount of egg or peanut) on the skin, then makes a small scratch or prick on the skin. Allergists usually do skin tests on a person's forearm or back. The allergist then waits 15 minutes or so to see if reddish, raised spots form. If so, there might be an allergy.

If someone might be allergic to more than one thing — or if it's not clear what's triggering a person's allergy symptoms — the allergist may skin test for several different allergens at the same time.

Skin tests may itch for a while. If your child has this test, the allergist might give you an antihistamine or steroid cream for your child to use after the test to ease itching.

When a skin test shows up as positive with a food, that only means a person might be allergic to that food. In these cases, doctors may want to do more tests, such as a blood test. This involves taking a small blood sample to send to a lab for analysis. The lab checks the blood for IgE antibodies to specific foods. If there are many IgE antibodies to a food, it's very likely that the person is allergic to it.

If the results of the skin test and blood test are still unclear, an allergist might do something called a food challenge. During this test, the person slowly gets increasing amounts of the potential food allergen to eat while the doctor watches for symptoms.

Because food allergies can trigger serious reactions in people, this test must be done in an allergist's office or hospital that has access to medicines and specialists to control these reactions. Most of the time, this type of test is done to find out if someone has outgrown a known allergy.

What Happens if a Test Shows an Allergy?

If your child does have an allergy, the doctor will work with you on a plan to keep your child safe. You’ll learn how to help your child avoid foods that aren’t safe. The doctor also will give you a prescription for emergency medicine (called epinephrine) to keep with your child all the time in case of a severe allergic reaction.

Reviewed by: Larissa Hirsch, MD
Date reviewed: January 2021