Question: How do you diagnose a food allergy?
Answer: The diagnosis of food allergy is a combination of a really good medical history -- to ask about the foods, the common foods, the temporal relation between the ingestion and the symptoms, the types of symptoms that they're having -- and then looking for IgE, which is the protein that you have to have to become allergic. The typical ways to look for IgE can be either by skin prick testing or some type of serum test -- most often used by the acronym RAST. Both of those look for IgE.
The interesting thing is that, if you don't have IgE to the food, you're not likely allergic. So it's a really good negative predictor of not being allergic. But, on the other hand, if you have IgE to, say, peanuts, it's not necessarily diagnostic that, for sure, you're allergic. You can have IgE and not be allergic to that particular food. So that's why it's important to combine the medical history and the diagnostic studies to help say, "Yes, your child's allergic," or "No, they're not allergic to that food."