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. "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.
Associate Professor Katie Allen said the new test could reduce the burden on clinicians and the health care system.
The following may help determine if you have a peanut allergy or if your symptoms are likely due to something else, such as food intolerance, a bout of food poisoning or some other condition. - Description of your symptoms. Be prepared to tell your doctor about your symptoms - such as exactly what happened after you ate peanuts, how long it took for a reaction to occur, and what amount of peanuts or food containing peanuts caused your reaction. - Physical examination. A careful exam can identify or exclude other medical problems. - Food diary. Your doctor may ask you to keep a food diary of your eating habits, symptoms and medications to pinpoint the problem. - Elimination diet. If it isn’t clear that peanuts are the culprit, or if your doctor suspects you may have a reaction to more than one type of food, an elimination diet may be needed. You may be asked to eliminate peanuts or other suspect foods for a week or two, and then add the food items back into your diet one at a time. This process can help link symptoms to specific foods. If you’ve had a severe reaction to foods, this method can’t safely be used. - Skin test. A skin prick test can determine your reaction to particular foods. In this test, small amounts of suspected foods are placed on the skin of your forearm or back. Your skin is then pricked with a needle, to allow a tiny amount of the substance beneath your skin surface. If you’re allergic to a particular substance being tested, you develop a raised bump or reaction. - Blood test. A blood test can measure your immune system’s response to particular foods by checking the amount of allergy-type antibodies in your bloodstream, known as immunoglobulin E (IgE) antibodies. For this test, a blood sample taken in your doctor’s office is sent to a medical laboratory, where different foods can be tested. However, these blood tests aren’t always accurate.
“Due to the rapid increase in rates of sensitisation to foods, allergy services are overwhelmed, and food challenge tests might be difficult to access.  This method would help alleviate the current strain and demand on clinical allergy services, with the allergy patient waiting times in excess of 18 months in many centres in Australia,” she said. 

Researchers say the test would also help minimise over-diagnosis, and would reduce the number of patients requiring referral to specialist services for confirmation of a food allergy, by using oral food challenges. Patients would simply need to visit a GP rather than require a referral to a specialist allergy clinic. “Due to the long wait times for specialist’s clinics, many clinicians are faced with the difficult task of having to assess the presence of food allergy based solely on a positive skin prick test or other available tests and must err on the side of caution and accept a diagnosis of ‘possible’ food allergy in these situations,” Dr Allen said “This approach can lead to over diagnosis of peanut allergy in the community and a potentially unnecessary burden on the health care system,” she said.      Diagnosis of peanut allergy is relatively straightforward when there is an obvious history of clinical reaction to peanut ingestion.  However, diagnosis can be more complicated in cases in which the clinical history is not clear or in children who have not yet been exposed to a food.
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