NAME: Dr. Tracy B. Fausnight
TITLE: Division chief, pediatric allergy and immunology
COMPANY: Penn State Hershey Children’s Hospital
YEARS IN FIELD: 10
Q: When should food allergy tests be performed?
A: I perform testing when a person has certain symptoms that occur shortly after eating, most often associated with a particular food. These symptoms may include a rash such as hives or eczema, mouth or throat itching, throat tightness or trouble breathing, vomiting, abdominal pain, and/or diarrhea, or a drop in blood pressure.
Q: What tests are commonly used for food allergies?
A: Both allergy skin testing and allergy blood testing are commonly used to test for food allergies. Skin testing involves gently placing a small amount of a food extract under the skin using a plastic needle-like device (I work with children so we do not use needles). If the patient is allergic, there will be redness and swelling at the skin test site. The testing is safe, the results are available within minutes, and they can be discussed at the same office visit. With blood testing, I can look at the level of specific allergy antibody to the food that is present. However, the results from this test are not usually available the same day.
Q: What does a positive skin or blood test indicate?
A: Positive tests, either by skin or by blood, only indicate the presence of allergy antibody to the food. The presence of allergy antibody alone does not mean that a person will have a reaction when eating the food. There are other reasons why these tests can be positive. The history is very important. An allergist is trained to interpret the skin testing, blood testing and history to help determine if there is a true food allergy.
Q: Do skin or blood tests predict how a person will react to a type of food?
A: Testing alone cannot predict how a person will react to a type of food. The larger the skin test reaction and the higher the amount of allergy antibody on the blood test can predict the likelihood of a reaction, but not the severity of a reaction. For example, people with larger skin test reactions to peanut are more likely to have a reaction when exposed to peanut as compared to people with small skin test reactions to peanut; however, they are not necessarily more likely to have more severe reactions.
Q: Are oral food challenges necessary to prove a food allergy?
A: If a person’s history is consistent with a food allergy and the testing supports the diagnosis, then an oral challenge is often not necessary. If the diagnosis is uncertain, then a food challenge is extremely important in determining if there is a true food allergy. Also, many children outgrow their food allergies. Food challenges are essential to see if a food allergy has been outgrown. A food challenge is the definitive test for food allergies — if a person can eat the food without any reactions, he or she is not allergic to it, no matter what the testing shows.
Interview conducted via email by The Patriot-News staff.