The number of people affected by food allergies has nearly doubled since the mid 1990s and continues to rise each year. The number of other food related issues and illnesses has also increased significantly in the last 15 years. Trying to figure out whether a reaction to certain foods is an allergy or some other issue can be challenging. But doctors have found that testing for reaction from immunoglobulin E (IgE) antibodies may help answer that question. IgE testing can potentially identify whether the reaction is an IgE mediated food allergy, a non IgE mediated food allergy or something else altogether. But what are IgE allergy tests, what do they test for and how predictive are they?
IgE Mediated and non IgE Mediated Allergies
Allergies are typically divided into three categories: IgE mediated, non IgE mediated and mixed. IgE are antibodies present in the body as part of the immune system. They react by entering cells and binding to proteins when foreign substances are introduced. The process causes histamine to be released, which results in inflammation, itchiness, hives and other symptoms of allergy. Allergic reaction that occurs because of IgE function is called IgE mediated allergies. Symptoms are usually immediate and can range from mild to severe.
Allergic reaction that happens without IgE involvement is called non IgE mediated. This type of allergic reaction is caused by other functions of the immune system that do not involve IgE antibodies. The exact mechanism of non IgE mediated allergic reaction is not well understood. Symptoms often do not appear for minutes, hours or even until the next day and generally affect the entire gastrointestinal system.
Since IgE testing is centered around the presence of IgE reactions to allergens, it is not useful in detecting non IgE mediated allergies.
What Is An IgE Allergy Test?
An IgE allergy test is designed to identify foods that cause a reaction from the IgE antibody. Doctors usually test for IgE reaction in one of two ways: “skin prick” or blood tests.
- Skin Prick tests take about 15-30 minutes in the doctor’s office and the results are immediate. A small amount of an allergen is placed under the skin through a tiny cut or prick. If a small bump that looks like a mosquito bite (called a wheal) appears, the test is considered positive for that allergen. Several skin pricks testing various allergens can be made during one session.
- Blood Tests are less sensitive and do not introduce the individual to any allergen. The test measures the amount of IgE antibody present when a specific food allergen is introduced. The results take about one to two weeks to obtain.
Accuracy of IgE Allergy Tests
Per FARE, IgE allergy tests are 50-60 percent likely to return a false positive for food allergy. This means a person could be identified as allergic to a particular food when in fact they are not. Some people may also get a false negative result. This means they test non-allergic when in fact they are. False negative results could lead to a disastrous outcome if a person does not realize they have a food allergy and eats that particular food. IgE allergy tests look for triggers to allergens that are related to IgE function of the immune system. But some food allergies don’t involve IgE antibodies to trigger a response. This is most commonly found with soy and milk allergies. So, testing negative for soy or milk allergies with an IgE test could occur even though the person is allergic.
Researchers and medical professionals have found that IgE allergy testing alone is not very reliable. But when added to a thorough patient history can be best predictor for determining and diagnosing food allergy.
Questions a doctor or allergist would likely ask include detailing the following:
- What symptoms occur after eating the food?
- How much of the food was eaten?
- How long after eating the food did symptoms occur?
- How frequently do reactions occur?
- What kind of medical treatment, if any, was administered?
- What are typical dietary choices and practices?
- What is the family history with allergies and other medical issues?
A detailed oral medical history could help identify non IgE mediated allergies that would be missed by an IgE blood or skin prick test, and can offset false positive results.
Have you or your child had IgE testing that missed an allergen? Have you been given a false positive? Share your experiences with food allergy testing in the comments below.