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 impr
