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Testing for Food Allergies

You may know exactly which foods you’re allergic to. But if you or your child have food allergies and aren’t sure which foods are to blame, allergy testing can help you identify them.

Make an appointment with a board-certified allergist. First the doctor will ask you questions about what you think you’re allergic to and your symptoms. Sometimes that’s enough to identify the problem food, or he may suggest allergy testing.

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Allergy testing can help your doctor figure out what you're allergic to, but it's not foolproof. After your tests are done, you'll need to work with your doctor to get the right diagnosis.

Skin Testing or Skin Prick Test

Skin testing is the most common and quickest food allergy test. Your doctor can test you for several foods at the same time.

First, the doctor puts a very small drop of liquid containing the food on your skin and pricks it. Then the doctor will watch for a reaction – a small bump that may get red like a mosquito bite.

If your skin reacts, you’re likely allergic to that food. You’ll want to avoid it and your doctor can talk with you about other treatment options. If you don’t react, good news! You’re probably not allergic to that food.

Blood Tests for Allergies

For this test, your doctor will take a sample of your blood and expose it to different types of allergens. You won’t learn the results right away. This test is often sent to a lab and results could take a week or more.

Doctors don't use it as often. They may use it if they have an idea of what you’re allergic to and it is only one or two specific things. Or they use this test if they are worried you have a severe allergy. That way, you don’t have to be exposed to the possible trigger.

Neither skin nor blood tests can accurately predict how severe a food allergy reaction may be.

A Controlled Food Challenge Test

This test isn’t done very often because it is dangerous for people with severe food allergies. 

When is it useful? Doctors will sometimes use this test to confirm a skin or blood test, or to see if a child has outgrown an allergy. It can be used to eliminate one specific food from the list, too. Why? Sometimes your skin might react to a food, but you wouldn't have symptoms if you ate it. 

Finally, in some cases a blood test may not be sensitive enough to find out your food trigger. A controlled food challenge can help sort it out.

For this test, you’ll go to your doctors’ office or a hospital. That way you can be watched closely in case you have a severe allergy attack.

Your doctor will give you food samples and watch you for a reaction. Or you may take capsules -- some with an allergen in it, some without. That way the doctor can be sure that it is the food causing the reaction. Never try a food challenge on your own because it can be very dangerous.

WebMD Medical Reference

Reviewed by Michael W. Smith, MD on November 12, 2012
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