Common allergy tests could yield false positives
Posted May 18, 2010
Chapel Hill, N.C. — A few years ago, Maria Servedio had a skin condition that her doctor thought might be the result of a food allergy. So, she was tested for allergies.
“I came up very high in a whole range of food, from things I was eating all the time to things that I was not eating very much,” Servedio said.
So, she stopped eating tree nuts, peanuts and all seafood.
The most common food allergy exams are a skin prick test to look for a skin reaction to certain foods or a blood test to look for certain antibodies associated with allergies. But neither test is more than 50 percent reliable.
“We are very well aware of the fact that tests that we have for food allergies are fraught with what we call ‘false positives,’” said Dr. Maya Jerath, an allergist at the University of North Carolina at Chapel Hill School of Medicine.
Jerath said blood tests are sensitive and accurate at detecting allergy antibodies, but “many people have allergy antibodies in their blood, but they’re not doing anything.”
Many people might be intolerant to certain foods like milk, for example, but it's not an allergy.
In cases where there is doubt, Jerath recommends food challenge tests.
“We actually feed you this food in a controlled environment, in a controlled manner to see if you truly react,” she said.
“When they did the food challenge, they found that I was completely fine with all kinds of nuts, even though the blood work did show that I have an allergy,” Servedio said.
Food challenges are more time-consuming than skin prick or blood tests, so it's a last option for many doctors.
The National Institute of Allergy and Infectious Diseases is trying to create guidelines for food allergy testing. A panel hopes to finish those guidelines by the end of next month.