Generally a food allergy is identified by signs and symptoms. Medical professionals are trained to recognize hives, swelling patterns, rashes, and other symptoms associated with allergic reactions.
Depending on your symptoms, your doctor may diagnose your allergies using one or more of a number of methods. Here are five tools your doctor is likely to use to conclusively determine which substances are causing your allergic symptoms.
Your first visit to the doctor for allergy symptoms will probably begin with a physical examination and a history. Your physician may ask you when your symptoms began, what sorts of foods you ate around the time they started, and what changes you may have experienced in your environment.
In almost all cases, your doctor will supplement the history with diagnostic testing. The history can help allergists pinpoint potential allergens to focus on, or to choose which testing methods might be most appropriate.
A prick test, or scratch test, is often used to test a number of potential allergens at one time. The allergist tests a number of allergens on the thin skin of the forearm or the back. A positive test will show as a hive, or wheal. An inconclusive prick test will usually be followed by a more sensitive test.
The RAST, or radioallergosorbent, test is a blood test that tests for IgE antibodies. It is often used in circumstances when a skin test would be difficult to perform (for example, in a patient with severe eczema or another skin condition) or where exposing the patient to an allergen might be unnecessarily risky (for example, in cases of suspected severe peanut allergies). A positive test result indicates that the body has produced antibodies to an allergen and is primed for a reaction.
An elimination diet can be undertaken in several ways, depending on the allergist supervising it, but the basic principle is the same: the diet begins with a limited set of foods that are deemed unlikely to cause a reaction. Other foods are added one by one over a period of days or weeks. While the elimination diet can be tedious, it can be an effective way to determine which substances are problematic when skin testing is inconclusive. It can also help diagnose food intolerances, which may cause problematic symptoms but will not show up on an allergy test.
Oral Food Challenge
An oral food challenge is risky and always carried out under close medical supervision, but will conclusively show the presence of an allergy. In a food challenge, patients ingest suspected allergens and are observed over a number of hours to determine whether they have an allergic reaction.