Cat allergen-induced blood basophil reactivity in vitro predicts acute human nasal allergen challenge responses in vivo

Background Basophil histamine release (BHR) to allergen has been used as a confirmatory test to support the clinical diagnosis of allergic disease. Objective Among subjects reporting respiratory cat allergy, we hypothesized that cat-induced BHR in vitro would predict nasal allergen challenge (NAC) response in that same individual. We therefore compared the magnitude of cat allergen-induced BHR to NAC outcome and serological measures of cat-specific IgE and the ratio of cat-specific IgE to total IgE. Methods Forty-two subjects with a history of cat allergy, positive cat puncture skin test (PST) and detectable cat-specific IgE (>0.1kAU/L, ImmunoCap) participated with consent. Subjects were grouped as positive or negative cat allergen-induced BHR, with a positive result defined as the release of 20% of the total cellular histamine content. The majority of subjects also underwent a NAC with a positive result defined as 5 total sneezes. Results Subjects with a positive compared with a negative cat allergen BHR had higher cat-specific IgE levels at 5.40±1.24kAU/L (n=25) vs. 1.55±0.73kAU/L (n=17, P=0.01) as well as a higher cat-specific IgE/total IgE ratio [6.1±1.4% (n=25) vs. 1.6±0.9% (n=17, P=0.01)]. Of the 31 subjects who underwent a NAC, a positive NAC was observed in 78% (18/23) with a positive cat allergen BHR compared with 37% (3/8) with a negative cat allergen BHR, giving a positive predictive value of 78% and a negative predictive value of 63%. The diagnostic sensitivity and specificity of a positive BHR to predict a positive NAC was 86% and 50%, respectively. Conclusions and Clinical Relevance A positive cat allergen-induced BHR is associated with higher cat-specific IgE levels, a higher cat-specific to total IgE ratio and is predictive of a positive cat-induced NAC [ClinicalTrials.gov NCT00604786].