Common Questions

The gold standard for food allergy testing is the oral food challenge, which is a medically supervised, gradual process of introducing a food allergen to a patient in order to diagnose or rule out a food allergy.

Both the blood test and the skin prick tests detect food-specific IgE. With the skin tests, the result is immediate, but the blood test result will take at least several days to arrive. Unlike the skin prick test, the blood test is not affected by antihistamines and can be performed for people with extensive rashes that prevent using skin tests.

Attempting to self-diagnose food allergies and interpreting results can be challenging. With food allergy tests, false positives and false negatives can occur. For this reason, you should always seek out a board-certified allergist to diagnose and treat your symptoms. Moreover, laboratories use various blood tests with different scoring systems. An allergist, however, is an expert and will be aware of the differences and know how to accurately interpret the results and explain to you what the results mean. Food allergy testing is an important part of making a diagnosis. However, an allergist has many tools that increase the accuracy of a diagnosis, such as taking into account your medical history, using the elimination diet, and using other methods of food allergy testing (such as skin testing).

About 50-60 percent of all blood tests and skin prick tests will yield a “false positive” result. This means that the test shows positive even though you are not really allergic to the food being tested. These results occur for two reasons: •The test may be measuring your response to the undigested food proteins. It is possible that after digestion, the food protein that enters your bloodstream is no longer detected by your IgE. •The test may be detecting proteins that are similar among foods but do not trigger allergic reactions. For example, if you are allergic to peanuts, your tests may show a positive response to other members of the legume family, such as green beans, even if eating green beans has never been a problem for you. Despite the high chance that the blood test or skin test may be positive despite there being no allergy, or, rarely, negative despite there being allergy, in the hands of an experienced allergist, blood and skin tests are extremely helpful. This is especially true when the results are interpreted in the context of your medical history. For example, if your history suggests that you have had several reactions after eating soy products, and the blood tests show a positive reaction to soy proteins, it is very likely that you do have a soy allergy. Your allergist may order additional tests, if necessary.

Many people with food allergies wonder whether their condition is permanent. There is no definitive answer. Allergies to milk, eggs, wheat and soy may disappear over time, while allergies to peanuts, tree nuts, fish and shellfish tend to be lifelong.

Eight foods make up more than 90 percent of all food allergies: egg, milk, wheat, soy, peanuts, tree nuts, fish and shellfish. Egg, milk, soy and wheat allergies are the ones we usually see being outgrown. About 80 percent of people with egg, milk and wheat allergies outgrow them, usually by age 16. About 20 to 25 percent of children with peanut allergies outgrow them, and about 80 percent who outgrow them will do so by age 8. Allergies to tree nuts, fish and shellfish may be tougher to outgrow and are often lifelong.