A New Test For Food Allergies

    Food allergy is reported commonly in children. Most food allergies in childhood cause mild symptoms and are outgrown. However, some food allergies cause more severe symptoms, even loss of consciousness and death. Doctors have always searched for more precise ways to diagnose food allergy.

     There are some ways of testing allergy that are simply worthless – like putting a substance under the tongue and then measuring changes in muscle strength. Legitimate allergy testing was originally done by injecting the allergic substance deep into the skin, but this could sometimes cause serious allergic reactions. This was replaced by the safer, superficial skin-prick method. Another way to accurately diagnose food allergy is to do a food challenge (allowing the child to eat the suspected food). In a food challenge, the food is given to the child under very closely controlled conditions in a doctor’s office. This method is not often used because it is difficult, dangerous and should only be done under a specialist’s care.

     In the late 1960’s, a protein produced in the body was found to be the substance that caused allergy. The protein is called IgE. Doctors began measuring the level of IgE in the patient’s blood to diagnose allergy and, over the years, our ability to measure this allergy protein has become more specific and accurate allowing us to test for allergy to individual foods. It is now the most popular form of allergy testing.   

    Although the blood test for allergy protein is widely accepted, it often gives false-positive results. This means that the test can report that the child has an allergy to a certain food, but when the child actually eats that food, he does not have an allergic reaction. False-positive results are common in children who have other allergic problems such as asthma and eczema. False-positive IgE tests also are the cause for many children to be diagnosed with multiple food allergies (“Johnny’s allergic to milk, eggs, nuts, chocolate, and fruit!”).

     False-positive tests are especially troublesome with the diagnosis of peanut allergy because peanut allergy is the most serious food allergy and frequently causes life-threatening reactions. A false diagnosis of peanut allergy can create unnecessary years of worry and difficulties in choosing the child’s diet.

     In May of 2011, the U.S. Food and Drug Administration allowed production of a much more accurate form of IgE allergy testing. It still involves drawing blood but it is more specific and can actually tell whether the child has the unique form of the protein that causes the allergic reaction. This testing is called molecular allergy testing and its use is spreading. Most doctors who test for allergy should be using it soon. It is the best way we have of testing for allergy and may eliminate the problems with false-positive results. If your child has been diagnosed with food allergy, talk to your caregiver about molecular IgE allergy testing.