Flow cytometric basophil activation test by detection of CD63 expression in patients with immediate‐type reactions to betalactam antibiotics

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Abstract
Background In this study, we used flow cytometry to determine the percentage of activated basophils that expressed the CD63 marker after in vitro stimulation by different betalactam antibiotics. The diagnostic reliability of the technique was assessed, as well as its correlation with specific IgE.Methods Fifty‐eight patients with clinical allergy to betalactam antibiotics and presenting positive skin tests to at least one of the allergens (minor determinant mixture (MDM), benzylpenicilloyl‐polylysine (PPL), penicillin, ampicillin, amoxicillin, cephalosporins) were tested. Thirty subjects non‐allergic to betalactams were also studied as controls. The flow assay stimulation test (FAST) uses flow cytometry to determine the percentage of basophils that express CD63 as an activation marker after in vitro stimulation with allergen. Double labelling with monoclonal antibodies anti‐CD63‐PE and anti‐IgE FITC was used.Results The allergic patients show a statistically greater number of activated basophils than the control subjects, after the incubation of cells with all the betalactams at various concentrations. The sensitivity of the technique is 50%, the specificity 93.3%, the likelihood ratio for a positive value 7.46 and the likelihood ratio for a negative value 0.54. In spite of having a greater sensitivity (37.9%) and specificity (86.7%) than CAP, differences between sensitivity and specificities of both techniques (CAP and FAST) do not reach statistical significance.Conclusion The basophil activation test is a particularly useful technique in the diagnosis of patients with IgE‐mediated allergy to betalactams and allows the identification of 50% of patients. Used in conjunction with CAP, it allows the identification of 65.5% of such patients.