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UK Scientists Targeting Peanut Allergy Test to Reduce False Positives, Overdiagnosis


NEW YORK (360Dx) – UK-based Medical Research Council said it has seen promising results in a study to validate the clinical utility of a lab test to diagnose peanut allergies.

In the study published last week in the Journal of Allergy and Clinical Immunology, MRC clinician scientists at King's College London reported that the test has 98 percent specificity, and avoids the risk of a patient receiving false-positives or having severe allergic reactions such as anaphylactic shock, a problem with existing methods of testing.

The approach, called the mast cell activation test, uses plasma samples and flow cytometry to evaluate the response of mast cells in patients suspected of having a peanut allergy reaction.

Mast cells in human tissue release histamine and other substances during inflammatory and allergic reactions. In their study, the MRC researchers found that the CD63 protein was the highest performing marker, as it is expressed on the surface of mast cells in response to a reaction to peanut allergies and is easily detected by flow cytometry, Alexandra Santos, an MRC clinician scientist at King's College London and the study's lead author, said in an interview.

Food allergy symptoms are triggered when allergens interact with the antibody immunoglobulin E, or IgE. The food allergens trigger symptoms such as skin reactions, itching, or constriction of the mouth, throat, and airways, as well as digestive problems such as stomach cramps, nausea, or vomiting.

Currently, doctors diagnose peanut allergy using a skin-prick or specific IgE test, but this can result in overdiagnosis or false-positives and it cannot differentiate between food sensitivity and true food allergy, Santos said.

Patients with an inconclusive test result undergo an oral food challenge. Allergists feed peanuts to patients in incrementally larger doses within a controlled setting in hospitals to confirm the allergy, but there's a risk of causing severe allergic reactions.

From a clinician perspective, the mast cell activation test would be useful as a second line lab test, where skin prick or specific IgE tests are not conclusive. "We can accurately diagnose many patients using clinical information, the skin test, and IgE, and they wouldn't undergo the oral food challenge. However, there is a proportion of patients — and in our clinic it reaches more than 50 percent — where we can't conclude whether the patient is allergic with enough certainty, and we have to refer them for food challenges," Santos said.

For their work, the MRC researchers used samples from 174 children who participated in allergy testing. They added peanut protein to mast cells in plasma samples, and found that, compared with actual clinical outcomes, their test identified peanut allergy with 98 specificity. Because the test is so specific in confirming a diagnosis, when it's positive, clinicians can be certain that an allergy is present, Santos said. Further, the test reflected the severity of peanut allergy; patients with more severe reactions had a higher number of activated mast cells.

Use of the new test would reduce by two-thirds the number of "expensive, stressful" oral food challenges, and it could be five times less expensive to implement in the UK than the oral food challenge, the researchers said. Further, it could help clinicians get around a constraint with implementing oral food challenges, Santos said: The challenges can be conducted only in a limited number of settings because they require that allergists and specialist nurses be available to monitor for adverse reactions and provide medical support when symptoms arise.

Peanut allergies are among the most common food allergies in children. In the UK, 5 to 8 percent of children have a food allergy and 1 in 55 children have a peanut allergy, according to estimates by the Food Standards Agency, a UK-based public health organization.  

"Peanut allergy is very common, especially in the US, UK, and Australia where the highest prevalence has been reported," Santos said. More patients are being referred to clinicians and specialists with suspicion of peanut allergy but identifying those that are truly allergic is tricky. "There are a lot of patients without a clear history because they haven't eaten peanuts before, or they have an allergic reaction in a more complex situation where they have eaten a lot of different foods or taken drugs at the same time, or the results contradict their medical histories," she said. On average, around 22 percent of school-aged children in the UK with a positive test to peanuts turn out to be allergic when they're fed the food in a monitored setting, Santos added.

A study involving 933 8-year-old kids, conducted by European researchers in 2010, concluded that most children do not have peanut allergies even when they are considered peanut-sensitized based on standard tests. With the advent of new treatments for peanut allergies, use of reliable in vitro tests rather than oral food challenges is desired to identify eligible patients and monitor clinical response to treatment, the researchers said at the time.

Santos noted that the MRC researchers are adapting their test to other foods, such as milk, eggs, sesame seeds, and tree nuts. They are also looking to apply it to monitor patients being treated for food allergies. In each case, these new applications would have to be clinically validated, Santos said.

For peanut allergy testing, however, the test has been adequately validated, she noted, and the scientists have been testing it in clinical samples for a few years.

The group is planning to work with an undisclosed diagnostic lab to commercialize the test, she said, adding that showing compliance with robust regulatory requirements and demonstrating standardization and quality assurance could push its commercial availability to two years or more.