Many who think they have food allergies actually do not.
A report, commissioned by the federal government, finds the field is rife with poorly done studies, misdiagnoses and tests that can give misleading results.
While there is no doubt that people can be allergic to certain foods, with reproducible responses ranging from a rash to a severe life-threatening reaction, the true incidence of food allergies is only about 8 percent for children and less than 5 percent for adults, said Dr. Marc Riedl, an author of the new paper and an allergist and immunologist at UCLA.
Yet about 30 percent of the population believe they have food allergies. About half the patients coming to Riedl's clinic because they had been told they had a food allergy did not have one.
For their report, Riedl and his colleagues reviewed all the papers they could find on food allergies published from January 1988 to September 2009, more than 12,000 articles. In the end, only 72 met their criteria, which included having sufficient data for analysis and using more rigorous tests for allergic responses.
People who receive a diagnosis after one of the two tests most often used — pricking the skin and injecting a tiny amount of the suspect food and looking in blood for IgE antibodies, the type associated with allergies — have less than a 50 percent chance of having a food allergy, the investigators found.
The paper, to be published today in The Journal of the American Medical Association, is part of a large project organized by the National Institute of Allergy and Infectious Diseases to try to impose order on the chaos of food allergy testing. An expert panel will provide guidelines defining food allergies and giving criteria to diagnose and manage patients. They hope to have a final draft by the end of June.
Part of the confusion is over what is a food allergy and what is a food intolerance, Fenton said. Allergies involve the immune system, while intolerances generally do not.
The chairman of the guidelines project, Dr. Joshua Boyce, an associate professor of medicine at Harvard and an allergist and pediatric pulmonologist, said one of the biggest misconceptions some doctors and patients have is that a positive test for IgE antibodies to a food means a person is allergic to that food. It is not necessarily so, he said.
The guidelines panel hopes its report will lead to new research as well as clarify the definition and testing for food allergies.
For now, Fenton said, doctors should not use the skin-prick test or the antibody test as the sole reason for thinking patients have a food allergy.
"By themselves, they are not sufficient," Fenton said.