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Reliable blood test (indirect BAT) for peanut allergy diagnosis

Published: January 21, 2022

The gold standard for the diagnosis of a peanut allergy is an oral food challenge (OFC), but this is a time-consuming, patient-unfriendly and expensive test. A relatively cheap new blood test is the direct Basophil Activation Test (BAT), which mimics an allergic reaction in vitro. A peanut allergic reaction is caused by binding of peanut protein to IgE immunoglobulin on the basophil (a type of white blood cell) which can stimulate the basophil to produce metabolites like histamine. The direct BAT for peanut has shown to be a promising diagnostic tool for replacing the OFC. However, disadvantages of the direct BAT are that a fresh blood sample has to be analyzed within 24h and about 10% of the tests give non-interpretable outcomes.

In The Journal of Allergy and Clinical Immunology: In Practice, Ruinemans-Koerts et al. evaluated and validated a new type of BAT, using donor basophils and only a small amount of patient serum (which can be stored for a long time); i.e. the indirect BAT. In 74 children, suspected of peanut allergy and eligible for an OFC, indirect BAT results for peanut extract, and the major allergen proteins of peanut, i.e. Ara h2 and Ara h6, were compared with the results of a double-blind, placebo-controlled food challenge (DBPCFC). The degree of reactivity and sensitivity of the basophils for peanut in the BAT were correlated to both the allergy status (allergic or non-allergic) but also to the amount of peanut protein which the patient could tolerate in the OFC.

The combined basophil reactivity for Ara h2 and Ara h6 showed the highest accuracy (94%) for the diagnosis of a peanut allergy, with positive and negative predictive values of 96% and 89%, respectively. Furthermore, the indirect BAT did not show any non-interpretable outcomes. The sensitivity of the basophils for Ara h2 significantly discriminated between patients who tolerated up to 0.4 g of peanut protein in the OFC and those who did not. This threshold of 0.4 g of peanut protein is, in clinical practice, the dose at which patients are expected to tolerate peanut traces.

In summary, the indirect BAT showed a high diagnostic accuracy for peanut allergy, and the authors propose that it is a promising alternative to the classical direct BAT and could lead to a reduction in expensive, time-consuming and patient-unfriendly OFC use. The indirect BAT enables a peanut allergy diagnosis to be made using a serum blood sample which can be stored for a long time and transported to a central laboratory.

The Journal of Allergy and Clinical Immunology: In Practice is an official journal of the AAAAI, focusing on practical information for the practicing clinician.

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