A Peanut Allergy Test That Is Both Safe and Accurate

Peanuts are the most common cause of fatal food-induced anaphylaxis, or severe allergic reaction, and allergy cases among children have risen sharply in recent years. Britain’s Food Standards Agency estimates up to one in 55 children have a peanut allergy. Canada’s estimates are similar: 1 in 50 children, according to Food Allergy Canada.

Nut allergies have grown significantly in the past few decades, with reactions to peanuts having some of the most significant and devastating effects. Unfortunately, the current options for testing a patient’s sensitivity to peanuts often produces a substantial number of false-positive results, and more alarming is the risk of triggering a deadly anaphylactic reaction.

Now, investigators at the Medical Research Council (MRC) & Asthma UK Centre in Allergic Mechanisms of Asthma in London have developed a new peanut allergy test that has a 98% specificity rate and provides no risk of allergic reaction. Findings from the new study were published in an article entitled “A Novel Human Mast Cell Activation Test for Peanut Allergy” in the Journal of Allergy and Clinical Immunology.

The new assay is a simple blood test that is five times more cost-efficient compared to the oral food challenge (OFC) – the current standard food allergy test – and could be adapted to test for other food allergies. Moreover, doctors diagnose peanut allergy using a skin-prick test or immunoglobulin E (IgE) test, but this may result in overdiagnosis or false positives, and it cannot differentiate between sensitivity and true food allergy.

“The current tests are not ideal,” explained lead study investigator Alexandra Santos, M.D., Ph.D., an MRC clinician scientist at King’s College London. “If we relied on them alone, we’d be overdiagnosing food allergies – only 22% of school-aged children in the U.K. with a positive test to peanuts are actually allergic when they’re fed the food in a monitored setting.”

When skin-prick and IgE test results are unclear, allergists rely on an OFC, which consists of feeding peanut in incrementally larger doses to a patient in a highly controlled setting in a hospital to confirm allergy to the food. While the test is the gold standard for diagnosing food allergies, there is a risk of causing severe allergic reactions. Now, the researchers have developed a safer, accurate blood test in the lab.

“The new test is specific in confirming the diagnosis, so when it’s positive, we can be very sure it means allergy,” Dr. Santos noted. “We would reduce by two-thirds the number of expensive, stressful oral food challenges conducted, as well as saving children from experiencing allergic reactions.”

The newly developed assay, called the mast activation test (MAT), could act as a second-line tool when skin-prick test results are inconclusive and before referring children and their families to specialists for an OFC.

Food allergy symptoms are typically triggered when allergens interact with an antibody called IgE. The food allergens activate IgE antibodies, triggering symptoms such as skin reactions, itching, or constriction of the mouth, throat, and airways, and digestive problems (such as stomach cramps, nausea, or vomiting). The current skin-prick test and IgE test, which have been in use for decades, measure the presence of IgE antibodies.

The MAT focuses on mast cells, which play a crucial role in triggering allergic reactions. Mast cells activate by recognizing the IgE in plasma and, in allergic patients, produce biomarkers associated with allergic reactions, which can be detected in the lab. The MAT is five times cheaper to conduct than the OFC, which requires an allergist and specialist nurses on hand to monitor for adverse reactions and provide medical support if symptoms arise.

In the current study, the MRC team used blood samples from 174 children participating in allergy testing – 73 peanut allergic and 101 peanut-tolerant. The scientists added peanut protein to mast cells to screen for IgE-mediated activation. The MAT accurately identified peanut allergy with a 98% specificity. (Specificity is a statistical measure in determining efficacy for diagnosis. The MAT rarely gives positive results in nonallergic patients.) The researchers also found the test reflected the severity of peanut allergy – patients with more severe reactions have a higher number of activated mast cells.

“We are adapting this test to other foods, such as milk, eggs, sesame, and tree nuts,” Dr. Santos added. “This test will be useful, as we are seeing more and more children who have never been exposed to these foods because they have severe eczema or have siblings with allergies. Parents are often afraid to feed them a food that is known to cause allergic reactions.