The Role of Food Allergy Tests
Food allergy tests help diagnose a specific allergy. They are used after someone has already shown signs of an allergic reaction. It is rare to do food allergy testing if someone has not shown symptoms of allergies.
After an allergy diagnosis, testing can be used to monitor whether a person is still allergic. Many food allergies go away over time, especially in children, and this kind of follow-up testing can help determine whether they can safely consume a food that they previously had an allergic reaction to.
When should testing be done?
Experts recommend food allergy testing only after symptoms of an allergy have occurred.
There is no single test to look for all food allergies, and tests can show signs of an allergy when no real allergic reaction occurs. This is known as a false positive result. Because a test that looks for all possible allergens can return many false positives, doctors normally order food allergy tests that look only for specific allergens based on your history of symptoms.
Types of Food Allergy Tests
Several different types of tests can be used to determine if you have a food allergy. Some tests involve direct exposure to a suspected allergen, and, for your safety, these tests must be done in a medical setting with a health professional.
- The skin prick test involves putting a drop of a possible allergen on your skin and then poking that area with a very small needle to let the substance get just beneath the top layer of skin. Even though you don’t eat the food, an allergic reaction is still detected in the skin. This test must be performed under careful medical supervision in case a severe reaction occurs.
- An allergy blood test measures levels of proteins called immunoglobulin-E (IgE) that can be elevated when you have an allergy to a specific food.
- An oral food challenge includes eating progressively larger amounts of a food at specified intervals over a period of a few hours. During the test, you are closely monitored by a doctor to see if there is an allergic reaction and to immediately treat a severe reaction if it occurs.
- Food elimination is not a strict testing method, but it may be employed to prepare for other tests and to see if avoiding a food reduces allergy symptoms. Food elimination generally requires carefully controlling your diet for a period of time to ensure that you have no exposure to one or more potential allergens.
While other types of tests may be marketed as food allergy tests, experts and professional organizations discourage their use because they are not proven to accurately determine when a person has a true allergy.
Getting Tested for Food Allergies
Allergy tests are usually ordered by a doctor. Before prescribing a test, the doctor asks about your symptoms and when they occured to try to identify the most likely allergen to test for. You may also be referred to an allergist, a specialist in diagnosing and treating allergies.
Many allergy tests must be performed under medical observation because of the possibility of a severe reaction. Tests with direct exposure are virtually always done in a hospital, clinic, or doctor’s office.
Blood tests for food allergies do not involve exposure and do not require the same precautions. A blood sample may be taken in a doctor’s office or laboratory and then sent for analysis.
At-home test kits are available for food allergy blood testing. These tests involve pricking your finger and putting one or more drops of blood on a test strip. You then mail the test strip to a laboratory that analyzes your blood immunoglobulin for signs of a potential allergy.
A positive test result alone cannot diagnose a food allergy. Instead, a doctor must evaluate your symptoms and health history along with any test results. When you discuss your symptoms with your doctor prior to testing, the doctor can look for the most likely allergens. However, this is not possible with at-home tests that look for a predetermined list of allergens.
Because allergy blood testing can return false-positive results, your doctor will likely want to do follow-up testing if your at-home test indicates that you may have an allergy.