A new blood test promises to predict which people will have severe allergic reactions to foods such as peanuts and shellfish. 

Physicians typically use skin prick tests (SPT) or blood tests that measure levels of allergen-specific immunoglobulin G (IgE); however, these tests cannot predict the severity of allergic reactions. Oral food challenges remain the gold standard for diagnosing food allergy even though the tests themselves can trigger severe reactions. 

Scientists at Mount Sinai Hospital (New York, NY, USA) and their colleagues took blood samples from 67 patients aged 12 to 45 years who also underwent a food challenge with a placebo or with peanut, tree nut, fish, shellfish, or sesame. Before the randomized food challenge, they collected blood from all patients. Double-blinded, placebo-controlled food challenges (DBPCFCs) remain the gold standard for diagnosing food allergies.

The doctors compared compare the utility of SPT wheal diameter, and allergen-specific (sIgE), allergen-specific IgG4 (sIgG4), total IgE (tIgE), sIgE/sIgG4 and sIgE/tIgE ratios, peanut component-specific IgE, and basophil activation in predicting outcome and severity of reactions at DBPCFCs. The SPT, sIgE, tIgE, sIgG4, and peanut component-specific IgE (if applicable) levels were measured. The upregulation of the CD63 protein on basophils in response to in vitro allergen challenge was analyzed by flow cytometry. Correlations between these measurements and DBPCFC severity scores were analyzed.

The SPT and sIgE showed a weak correlation with DBPCFC severity scores, but tIgE and sIgG4 did not. The sIgE/sIgG4 ratio differentiated between positive and negative reactions but did not correlate with DBPCFC severity scores. A low positive correlation was seen between DBPCFC severity score and the peanut component antibody Ara h 2 IgE, whereas a low negative correlation with Ara h 8 IgE was observed. Basophil activation was positively correlated with DBPCFC severity scores. This finding provides evidence that basophil activation testing (BAT) can reduce the need for food challenges not only for peanut, but also for tree nut, fish, shellfish, and sesame and perhaps for other foods.

Ying Song, MD, the lead author of the study said, “While providing crucial information about their potential for a severe allergic reaction to a food, having blood drawn for BAT testing is a much more comfortable procedure than food challenges. Although food challenges are widely practiced, they carry the risk of severe allergic reactions, and we believe BAT testing will provide accurate information in a safer manner.” The study was published in the April 2015 issue of the journalAnnals of Allergy, Asthma & Immunology.