Published Online: July 25, 2014
The majority of patients who test positive to being allergic to peanut, using either a skin prick test (SPT) or specific IgE (sIgE), are not actually peanut allergic. In equivocal cases, oral food challenges (OFC) need to be performed to clarify a patient’s allergic status. OFCs consist of giving the food in incremental doses in a controlled environment to confirm whether a patient develops an allergic reaction, which is potentially severe. This is currently the gold-standard for the diagnosis of peanut and other food allergies. Apart from the risk involved, given the increasing prevalence and awareness about allergy tests and peanut allergy, specialized centers have difficulties in responding to the increasing OFC demand and over-reliance on SPT and sIgE in the diagnosis of peanut allergy is common.
In a study recently published in The Journal of Allergy and Clinical Immunology (JACI), Santos and colleagues assessed the utility of a new diagnostic test, the basophil activation test (BAT), in the diagnosis of peanut allergy. Basophils are immune cells involved in peanut allergic reactions, including anaphylaxis. The BAT is a flow cytometry-based test where the reaction of basophils to peanut allergens is assessed in a test tube and can be seen as an in vitro surrogate of OFC. The authors performed BAT in 104 children—including 43 peanut allergic and 61 peanut tolerant (of whom 59% had a positive SPT or sIgE to peanut)—in parallel with other allergy tests, and determined diagnostic cut-offs using the allergic status (i.e. allergy versus tolerance) as the reference-point. The identified optimal cut-offs were validated in a second independent population of 65 patients recruited from a second specialized clinic in London and from an ongoing study with participants from different parts of the United Kingdom. Considering the possibility of applying BAT to clinical practice in the future, Santos et al evaluated the diagnostic performance of BAT in combination with the other allergy tests and its impact in the number of OFC.
BAT made an accurate diagnosis of peanut allergy or tolerance in 97% of cases. It showed 98% sensitivity, 96% specificity, 95% positive predictive value and 98% negative predictive value in the primary study population and 83% sensitivity, 100% specificity, 100% positive predictive value and 90% negative predictive value in the validation population. The high specificity of BAT underscores its value compared to conventional allergy tests which have high sensitivity but not as high specificity in diagnosing food allergy. The most difficult cases of clinical and laboratory data (n=44) were reviewed by three consultants looking at clinical history, SPT, specific IgE to peanut and components, and these consultants were asked to diagnose allergy, tolerance, or opt for a challenge. There was poor agreement between consultants’ decisions, and BAT was able to reliably diagnose these particularly difficult cases. Overall, on its own, BAT ensured a two-third reduction in the number of OFCs. Using a 2-step diagnostic approach, where BAT was performed only in the cases where SPT or sIgE were equivocal, which would involve a lower number of BAT performed, BAT dramatically reduced the number of OFCs up to 97%.
Santos and colleagues concluded that BAT to peanut can be performed in cases where conventional allergy tests are inconclusive before deciding to refer a patient for an OFC. When applied to clinical practice, BAT could significantly reduce the need for OFC and improve the diagnosis and management of patients with suspected peanut allergy.
The Journal of Allergy and Clinical Immunology (JACI) is an official scientific journal of the AAAAI, and is the most-cited journal in the field of allergy and clinical immunology.