Allergy Tests

What are allergy tests?

Allergy tests are tests your healthcare provider can do to find what is causing allergy symptoms. Examples of common allergy symptoms are sneezing, watery eyes, runny nose, itching, swelling, hives, stomach cramps, and diarrhea.

Why are these tests done?

Substances that trigger allergy symptoms are called allergens. Allergy testing is the most precise way to find what allergens are causing your symptoms. They can help you know what you are allergic to. Then you will know what substances you should try to avoid.

You may need allergy tests if you have allergy symptoms that you cannot control with medicine. If the allergy tests can identify the things you are allergic to, then your provider may recommend treatment with allergy shots. A mixture that contains the allergens identified by your tests can be used in the shots. Your allergies can then be treated by injecting the mixture into your skin in tiny but increasing amounts over the course of many months. The shots will help you have fewer symptoms when you are exposed to allergens.

How do I prepare for these tests?

• You may need to avoid taking certain medicines before the tests because they might affect the test result. For example, you may need to stop taking any antihistamines several days before the tests.
• Talk to your healthcare provider before the tests if you have any questions.

How are the tests done?

The 4 main kinds of tests used to identify allergy triggers are:

• skin tests
• blood tests
• food challenges
• elimination diets

Skin tests: A test called the skin prick test is the most common type of skin test. For this test, a drop of allergen extract (liquid) is put on the skin and then the skin is pricked with a small needle through the drop. This lets the allergen get under the skin. The test can also be done with a pricking device that has been presoaked in the allergen extract. Only the top layer of skin is pricked. The test is usually done on the back or the arm. The skin test is ready to check in about 15 minutes. If you are allergic to the allergen in any of the extracts, a red bump that looks like a hive or mosquito bite will appear at the spot where the extract was placed. If the prick test is negative or the test results are not clear, a similar but more sensitive test called an intradermal test may be done. For the intradermal test, a very small amount of allergen is injected under the skin.

Blood test (RAST test): This test checks a sample of your blood for antibodies your body may have made against different allergens. If the test finds antibodies to certain allergens, you may be allergic to those substances.

Food challenges: To check for food allergies, your healthcare provider may want you to do a food challenge test. For this test, you are given gradually increasing amounts of a food while your provider watches for symptoms. This test should be done only by a trained professional who is ready to treat you if you have a serious reaction to the food. Some stomach or intestinal allergies cannot be identified with the skin and blood tests, so a food challenge test may be the only good way to diagnose the allergy.

Elimination diet: For another check of possible food allergies, your healthcare provider may want you to avoid eating certain foods for a few weeks to see if allergy symptoms go away. During this time, you will need to keep a record of the foods that you eat and any symptoms you have. The diet is followed until all allergic symptoms are gone. Foods are then added back to the diet one at a time. If symptoms come back, it may mean that the most recently added food is the one you are sensitive to.

What do the test results mean?

If the skin or blood test is negative for an allergen, then you probably do not have an allergy to that substance.

If the skin test is positive for an allergen, it may mean you are allergic to that food. However, sometimes a test can be positive even if you are not allergic to the food. The positive test result can be wrong sometimes because:

• You can sometimes continue to have a positive test result for many years to an allergy you have outgrown.
• You are allergic to a different substance that has some components similar to the allergen you were tested for. For example, you might have a positive test for soy if you have peanut allergy, or a positive test to wheat if you have a grass pollen allergy.

Test results are only one part of a larger picture that takes into account your medical history and current health. Sometimes a test needs to be repeated to check the first result. Talk to your healthcare provider about your results and ask what the results mean for you.

What happens after the tests?

An allergy specialist will interpret the results of the tests and suggest ways your allergy might be treated. Be sure to discuss your results with your healthcare provider and make sure you understand how best to care for your allergy symptoms.

For more information contact:

• The Food Allergy & Anaphylaxis Network
  Phone: 800-929-4040
  Web site: http://www.foodallergy.org
• The American Academy of Allergy, Asthma & Immunology
  Phone: 800-822-2762
  Web site: http://www.aaaai.org.