BOSTON—New ways of diagnosing food allergies are on the horizon, with allergy experts hoping that it might be possible one day for many patients to avoid the traditional food challenge test (FCT).
A recently published Italian study, discussed at the 2010 Annual Meeting of the American Academy of Otolaryngology-Head and Neck Surgery, held here Sept. 26-29, found that examining the levels of certain proteins could help with allergy diagnosis (D’Urbano LE, Pellegrino K, Artesani MC, et al. Clin Exp Allergy. 2010;40(10):1561-1570). Researchers found that when the traditional blood test for cow’s milk and hen’s egg allergy is combined with a new diagnostic blood test called component resolved diagnosis (CRD), the diagnostic accuracy approaches that of the traditional double-blind, placebo-controlled, food challenge test.
“Is there a way to avoid what’s always been the gold standard for food allergies, which is double-blind, placebo-controlled food challenge, which is time-consuming, expensive and can be somewhat dangerous?” said Karen Calhoun, MD, professor of otolaryngology-head and neck surgery at The Ohio State University College of Medicine in Columbus, who discussed the study in her presentation.
In the study, the researchers reported that the “ideal” in vitro test should allow patients and their doctors to avoid the FCT. The study included 104 children, some with allergies to milk and others with allergies to eggs.
Researchers found that the ImmunoCAP (ICAP) test, a blood test commonly used to detect allergies, was 93 percent predictive of a positive food allergy test result when a threshold of at least 16.6 kU/L was met for cow’s milk immunoglobulin E (IgE). But when that level was below 16.6 kU/L, the test was only 43 percent predictive.
Researchers divided this second group based on their levels of the allergen Bos d 8 and found that 14 out of 15 patients with levels above 0.6 ISAC standardized units (ISU) had also been positive in food challenge tests.
Looking at specific allergens may be a way to attain more accuracy than would be possible with the ICAP test alone—without having to do a food challenge test, Dr. Calhoun said. “This is honing in on something that is clinically useful,” she said.
That microarray-based test might make the process more tolerable to children, said Maria Veling, MD, associate professor of surgery in the division of otolaryngology-head and neck surgery at the University of Kentucky in Lexington. “The big advantage of that test is that it requires less blood to be performed,” she said. “And this is very helpful when you’re trying to test children.”
This and other advances come as food allergies continue to rise. According to Dr. Calhoun, 2 to 3 percent of adults and 6 to 8 percent of infants have food allergies, including 35 percent of children with moderate to severe atopic dermatitis. In addition, 45 percent of young children have asthma. The presenters pointed out, however, that about 25 percent of adults think they have a food allergy.
“Food allergy is on the increase and we’re not really sure why,” Dr. Calhoun said. “There certainly is a hereditary component, but there’s also an environmental exposure component.”
Most allergies in children eventually go away. Dr. Calhoun pointed to research showing that egg allergies are resolved in 75 percent of cases by age seven, while milk allergies are resolved 76 percent of the time by age five. Wheat allergies are resolved 80 percent of the time by age five, and 20 percent of peanut allergies are resolved by age five.
Several of the presenters emphasized that accurately diagnosing a patient without using an FCT has been tricky because skin prick tests and in vitro tests are not very specific; only about 50 percent of those with positive results actually have allergies. But if the result is negative, there is a high probability that a patient does not have the allergy.
“Our goal, of course, is to improve our diagnostic ability so that we are able to correctly identify those patients affected by food allergies,” Dr. Veling said.
Although other tests being investigated include patch testing, this is not yet recommended because of insufficient evidence supporting its efficacy.
Non-standardized tests that have not been shown to be of value in the diagnosis of food allergy, according to Dr.
Veling’s review, include: Basophil activation, assays that measure activation markers on basophils; the measure of inflammatory markers in blood and feces to predict an allergic reaction; and IgE-positive cell count in the gastrointestinal tract or evaluation of gut mucosal responses to allergen instillation during endoscopy.
She said that intradermal skin testing is not recommended at this time because it is potentially dangerous and overly sensitive and has an unacceptable rate of false-positive reactions.
Work is also underway on methods to prevent food allergies and treat them once they’re found. A study in the United Kingdom, Learning Early About Peanut Allergy (LEAP) is looking at the effects that peanut products have in children who are considered to have a high risk of developing peanut allergies, said William Reisacher, MD, an assistant professor of otorhinolaryngology at Weill Cornell Medical College in New York City and director of the Allergy Center there.
The children, aged four to 10 months, already have eczema or an egg allergy, making them more likely to develop a peanut allergy; one group is fed a peanut snack three times a week, and another group is not. Rates of peanut allergies will be compared after five years.
Researchers are also investigating how to desensitize patients to the antigens causing their allergies, Dr. Reisacher said.
In 2009, a study looked at 29 patients, aged one to 16, who were on maintenance dosing for 36 months. Ultimately, 93 percent of the patients were able to tolerate 13 peanuts with only mild symptoms (Jones SM, Pons L, Roberts JL, et al. J Allergy Clin Immunol. 2009;124(2):292-300). A follow-up study is scheduled for 2012, Dr. Reisacher said.
Future work on desensitization is likely to concentrate on the role of flavonoids, genetically modified antigens, overlapping peptide vaccines and plasmid DNA-encoded vaccines, he said.
“Lots of things are happening in this field,” he said. “But it seems like we have more questions, actually, than answers.”