April 4, 2011 (San Francisco, California) — A new laboratory test that measures reactions to protein components of peanuts (ImmunoCAP, Phadia) is more effective at identifying patients with severe allergies than current diagnostics, according to researchers here at the American Academy of Allergy, Asthma and Immunology 2011 Annual Meeting.
"This test is a much better discriminator for true peanut allergy than currently used peanut Ig [immunoglobulin] E measurements," said study author Robert Wood, MD, professor of pediatrics and chief of pediatric allergy and immunology at Johns Hopkins Children's Center, Baltimore, Maryland. The study by Dr. Wood and colleagues is the first to definitively demonstrate the clinical utility of ImmunoCAP's values for antibodies to peanut components in a population in which peanut allergy is in question, he noted.
The new test for peanut components has not yet been approved by the US Food and Drug Administration, but it is likely that the test will be licensed within the next year, Dr. Wood said.
In the study of 61 children at Johns Hopkins Pediatric Allergy Clinic, patients were tested for IgE antibodies to 4 peanut protein components — Arah1, Arah2, Arah3, and Arah8 — between 2003 and 2010. All patients in the study had previously tested positive for peanut allergy with peanut-specific IgE at a level of 0.35 kUa/L or more, and underwent a peanut challenge during the course of the study.
Results indicated that peanut-specific IgE levels were not a reliable indicator of whether a child failed or passed a peanut challenge. Children who failed the peanut challenge had a median PN-IgE level of 1.32 kUa/L; for those who passed the challenge, the level was 1.34 (P = .50).
However, IgE levels for one of the proteins, or anti-Arah2 levels, were significantly higher in patients who failed the peanut challenge than in those who passed (P < .01). Anti-Arah2 levels could correctly identify up to 86% of those who failed the peanut challenge. In addition, serum IgE anti-Arah8 levels were higher in patients who passed the challenge (P < .01), and Arah2-specific antibody levels (or negative test results to Arah2) correctly identified 94% of patients able to pass a peanut challenge.
"A higher IgE level against Arah8 was predictive of true peanut allergy," Dr. Wood said.
The new test for peanut components is an exciting and promising addition to diagnostics for peanut allergy, particularly because those with severe allergies can experience life-threatening symptoms, said allergist and immunologist Jeffrey Factor, MD, associate clinical professor of pediatrics at the University of Connecticut School of Medicine in Farmington and medical director of the New England Food Allergy Treatment Center in West Hartford, Connecticut. Dr. Factor also runs a research center in Connecticut, where he is testing desensitization strategies for treating peanut allergies. He was not involved with the peanut allergy diagnostic research at Johns Hopkins.
"Until now, there's really been no way of knowing how severe or persistent a food allergy could be. Peanut allergy was diagnosed based on skin tests or general blood tests. But by looking at these component diagnostics, we can see that patients who react to proteins such as Arah2 are more likely to have severe and persistent allergy," he said.
Component food allergy tests could be used to identify patients who could benefit from desensitization with oral immunotherapy — a treatment in which tiny amounts of an allergen are used to gradually build up a patient's tolerance over time, Dr. Factor noted. "If we're able to measure reactions to peanut components, we may be able to tell which patients could have a potentially life-threatening allergy, and which allergies should be taken more seriously than those in patients who just react to Arah8," he said.
Dr. Wood and Dr. Factor have disclosed no relevant financial relationships.
American Academy of Allergy, Asthma and Immunology (AAAAI) 2011 Annual Meeting: Abstract 267. Presented March 19, 2011.
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