Test to improve peanut allergy diagnosis

Researchers from the Murdoch Childrens Research Institute and the University of Melbourne have identified a new way to accurately test for peanut allergy.

It is hoped the test will be more cost effective and convenient than standard approaches and minimise over-diagnosis of peanut allergy in the community.

Currently, an oral food challenge is the standard for diagnosing peanut allergy, and while an oral food challenge is definitive in diagnosing patients, it is time-consuming, costly and patients risk severe reactions such as anaphylaxis.

The new test researchers have identified uses part of the peanut protein called 'Arah2' and involves a two-step screening process. Researchers found they could perform a blood test, followed by the Arah2 test, which was more accurate and highly predictive than using one of the tests alone. They found the two step testing process reduced the need for oral food challenges by four-fold.

Co-lead researcher, Thanh Dang, a University of Melbourne PhD student based at the Murdoch Childrens Research Institute, said the new test has many benefits.

"By reducing the number of oral food challenges, this helps prevent many peanut allergics undertaking the unnecessary risks involved."

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.