Can most food allergies be outgrown?
Children with allergies to cows' milk, egg, soy and wheat usually outgrow their allergy by the time they are five years old. If the children successfully avoid eating the food, they improve their chances of outgrowing the allergy. Other foods like peanuts and tree nuts, as well as seafood, tend to be lifelong food allergens for people. However, there have been two studies that have shown that as many as 19 percent of children outgrow their peanut allergy, particularly if they were diagnosed by their first birthday and if they have sustained successful peanut avoidance since then.
How does an allergist or an immunologist diagnose food allergy?
The approach to diagnosis begins with taking a thorough history focusing on the reactions. Then we do a physical examination to see whether there are other signs of an allergic process, such as the presence of atopic dermatitis.
If we feel that the likelihood of allergy is there, then the next step generally is to proceed with allergy skin tests. Allergy skin tests can be performed in as little as 20 minutes. They aren't painful. We do a test called a percutaneous skin test, which introduces the allergen into the very superficial layers of the skin. We always try to select the allergens that we think are relevant based on history. With the skin test, we're looking for whether or not there is a reaction characterized by an area of swelling surrounded by redness. Negative skin tests essentially rule out that a food allergy exists. Positive skin tests are harder to interpret, since these tests have a false positive rate of 60 percent.
If the skin test is negative but we have a strong impression that an allergy is present, we may do additional testing by doing a blood test called RAST. That is a way to measure the amount of allergy antibody for that particular allergen.
When do you do a food challenge?
A food challenge simulates the true exposure because it's a procedure where the individual eats the food under medical observation. A food challenge may be performed to confirm the diagnosis. Sometimes we do food challenges where we hide the identity of the food from the individual eating it, their family and even from the physician and nurse so there won't be any bias.
Sometimes we need to do a food challenge if we end up with a lot of positive skin tests, and we aren't sure which one is the culprit. Other times we use a food challenge to assure a family that a particular food is not the culprit.
Once a food allergy has been diagnosed, what steps do you take at that poin?
Once we have established a diagnosis, we implement education and counseling for the family, and a medical treatment plan. Education is really critical because it's so difficult to implement an avoidance diet. We also refer the families to national (Food Allergy and Anaphylaxis Network) and local support groups. We also provide families with a written emergency healthcare plan so that in the event of an accidental exposure, they have a reference. We try to review the different scenarios that could play out and how we would like the family to handle those scenarios.