Optimization of Basophil Activation Test in the Diagnosis and Qualification for Allergen-Specific Immunotherapy in Children with Respiratory Allergy to the House Dust Mite Dermatophagoides pteronyssinus

The aim of this study was to optimize a basophil activation test in the detection of allergy to the house dust mite <i>Dermatophagoides pteronyssinus</i> in children with allergic respiratory diseases. This study involved 32 cases, 13 girls and 19 boys aged 4-17 years, with perennial asthma or allergic rhinitis caused by <i>D. pteronyssinus</i>. The control group consisted of 13 girls and 19 boys aged 4-17 years with seasonal allergic asthma or rhinitis provoked by Timothy or birch pollen. House dust mite (HDM) allergy was excluded in the controls based on their medical history, skin prick test (SPT) results and sIgE determination. In all patients, a basophil activation test (BAT) was performed with five dilutions of <i>D. pteronyssinus</i> allergen (the dilution series ranged from 22.5 to 0.00225 ng/mL). The results were analyzed by using the receiver operating characteristics (ROC) to determine the optimal allergen concentrations, outcome measures and cut-off points that would differentiate most accurately between HDM-allergic and non-allergic patients. As a "gold standard", criteria for allergen-specific immunotherapy with <i>D. pteronyssinus</i> or respective pollens were applied by an experienced pediatric allergist following the guidelines of the European Academy of Allergy and Clinical Immunology. The highest diagnostic efficiency was yielded by the protocol assuming a cut-off value of 9.76% activated basophils after activation with a single allergen concentration of 2.25 ng/mL (sensitivity 90.6%, specificity 100%). This protocol yielded 3 (4.7%) misclassifications, all false negative, when compared with the "gold standard". There was a strong correlation with the BAT results at 22.5, 2.25 and 0.225 ng/mL (respectively r = 0.90 and r = 0.78, <i>p</i> < 0.001), as well as between the BAT at 2.25 ng/mL and SPT (r = 0.82, <i>p</i> < 0.001) and between the SPT and sIgE levels (r = 0.78, <i>p</i> < 0.001). High cross-reactivity between <i>D. pteronyssinus</i> and <i>D. farinae</i> was confirmed based on the BAT at 22.5 ng/mL (r = 0.82, <i>p</i> < 0.001). In conclusion, the BAT showed very good concordance with the result of a meticulous process of decision-making that combined validated allergy tests (SPT, sIgE) with expert guidelines, specialist knowledge and experience. Facing the risk of the incorrect qualification of patients for costly, long-lasting and potentially risky allergen-specific immunotherapy, the inclusion of a basophil activation test into diagnostic process seems fully justified.