Leaderboard Ad

Update on Food Allergy Science

“This is an exciting time for physicians who take care of patients with food allergies,” said William R. Reisacher, MD, Weill Cornell Medical College, New York. “This is a rapidly evolving area with new evidence and new information coming out every year.”

Dr. Reisacher moderated a special miniseminar, “Food Allergy 2013: State of the Science,” on Monday morning. New information on food allergies can have an immediate impact on clinical practice.

Adverse reactions to food can stem from non-immune and immune sources, said Karen H. Calhoun, MD, Ohio State University Wexner Medical Center in Columbus, OH. Most patients and parents jump to the conclusion that they have either food poisoning or allergies.

“More people think they have food allergies than really do,” she said. “It is true that food allergies are increasing, but the incidence in infants is four percent to six percent and just two percent to three percent in adults. Fortunately, a lot of allergies in children resolve as they grow older.”

In fact, most allergies to egg, milk, wheat, and soy resolve during childhood. These four foods, along with tree nuts, peanuts, shellfish, and fish, account for 90 percent of all food allergies.

Food allergies are essentially a failure of normal oral tolerance mechanisms. Oral antigen exposure typically leads to tolerance, she explained. The gut mucosal immune system favors a suppressive immune response, which yields tolerance and oral feeding usually causes antigenic immune tolerance.

The good news is that sensitivity does not equate to allergy. Up to two percent of U.S. children have detectable anti-peanut IgE, Dr. Calhoun said, but only a quarter have a clinical reaction to peanuts.

The most recent guidelines on allergy testing from the National Institutes of Health highlights the difference between sensitization and allergy, continued Cecelia Damask, DO, Lake Mary Ear, Nose, Throat & Allergy in Orlando, FL. Diagnostic testing alone, whether skin prick testing or serum IgE, cannot be the sole basis for diagnosing food allergy.

“Testing can indicate sensitivity, but an oral challenge is a more effective method to establish the presence of a food allergy,” she said.

The problem, she continued, is that too many individuals who order allergy testing do not understand that tests reveal only sensitization. And too few clinicians conduct food challenges to verify allergy diagnoses.

Allergy testing is also incapable of predicting the significance of cross reactivity or the severity of a reaction. All current allergy tests are imperfect, with high sensitivity, poor specificity, high negative predictive value, and low positive predictive value.

The relative insensitivity of allergy testing could change. Most foods contain multiple allergens, but individuals tend to be allergic only to one or two epitopes. Component Resolved Diagnostic Testing, or CRD, tests for sensitivity to specific epitopes and has shown very good results in Europe.

Peanuts, for example, contain multiple allergenic proteins, but rAra h 2 appears to be a major source of peanut allergy. Early clinical results found that rAra h 2 above 1.96 ku/L offers 99 percent specificity and 96 percent positive predictive value. Similar trials in different populations have produced similar results.

“CRD is still an evolving concept,” Dr. Damask said. “Results seem to be population-specific. More studies need to be done.”

Recent research is also changing management strategies. While clinicians still work on prevention, avoidance, medications, and desensitization, Dr. Reisacher noted, tolerance is the ultimate goal.

Early introduction of potentially allergenic foods appears to reduce the risk of subsequent food allergies. The American Academy of Allergy, Asthma and Immunology advises the introduction of complementary foods between four and six months of age and warns that the delayed introduction of solid foods, especially highly allergenic foods, increases the risk of food allergy or eczema.

“There is an early window to develop oral tolerance,” Dr. Reisacher said. “It is very important to expose kids to allergenic foods early. Delayed introduction of solid foods is associated with more food allergies.”