Blood Test Could Help Predict Nut Allergies

New research on the ability of particular peanut proteins to trigger IgE reactions in blood samples may reduce the need for potentially dangerous oral challenges.

Blood tests designed to detect allergies have been around for decades, but those that are most commonly used today are prone to significant numbers of false positives and false negatives. Skin-prick tests are also error prone and slightly dangerous as well.

Researchers from Helsinki, Finland studied the efficacy of blood tests that exposed patient blood samples to individual peanut proteins rather than small quantities of peanut and found that reaction to certain proteins predicted peanut allergies better than reaction to whole peanut.

The double-blind placebo-controlled study began with 102 patients, aged 6 to 18, who exhibited signs of possible peanut sensitization that ranged from mild discomfort to anaphylaxis. Oral peanut challenges produced severe reactions in 25 of those patients, moderate reactions in 36 others, and mild reactions in 8 more people. The remaining 33 patients tested negative for allergies.

The researchers then bombarded blood samples from each patient with 6 different peanut proteins — Ara h 1,2,3,6,8 and 9 — and then tested allergen activity in the blood samples with IgE-microarray inhibition.

The best marker for moderate to severe allergies was a patient’s specific IgE to Ara h 6 (area under the curve [AUC], 0.98; 95% confidence interval [CI], 0.96-1.00). When specific IgE to Ara h 6 and Ara h 2 were measured together, blood tests successfully detected all severe allergies. Specific IgE to Ara h 8, on the other hand, had no diagnostic value at all (AUC 0.42; 95% CI 0.30-0.52)

“Co-sensitization to Ara h 2 and Ara h 6 was associated with severe reactions distinguishing severe allergy from mild symptoms,” the study team wrote in the European Journal of Allergy and Clinical Immunology. “Component-resolved diagnostics reduce the need for oral challenges in peanut allergy.”

Previous research into blood tests that rely upon component resolved diagnostics for the detection of peanut allergies have typically found that they out-perform blood tests that are typically used in clinical practice.

A study published in 2010 by the Journal of Allergy and Clinical Immunology found that only 22.4% of 110 8-year-olds who tested positive for peanut sensitization via skin pricks, and standard blood tests were actually allergic to peanuts (95% CI, 14.8%-32.3%).

Another study published 2 years later in the same journal used a sample of 200 infants — half of them with peanut allergies and half of them with no peanut allergies — to compare the sensitivity of whole peanut testing and testing that used Ara h 2 alone.

“The sensitivity of Ara h 2 sIgE is 60% (95% CI, 50% to 70%), correctly identifying 60% of subjects with true peanut allergy compared with only 26% correctly identified by using whole peanut specific IgE,” the study authors wrote. “We report that when using a combined approach of plasma specific IgE testing for whole peanut followed by Ara h 2 for the diagnosis of peanut allergy, the number of OFCs required is reduced by almost two thirds.”

A year after that, a third study published in the Journal of Allergy and Clinical Immunology, reached a similar conclusion. It found that specific IgE to Ara h 2 alone could predict 50% of all peanut allergies and that incorporating this observation into allergy diagnosis could reduce the need for peanut challenges by at least 50%.

None of the 3 studies used Ara h 6 in tests, so if that protein proves even more valuable in predicting actual peanut allergies — particularly when used in conjunction with Ara h 2 — it could reduce the need for oral challenges even more.