Potential role of the cellular allergen stimulation test (CAST) in diagnosis of allergic bronchopulmonary aspergillosis (ABPA) in cystic fibrosis

Abstract

Allergic bronchopulmonary aspergillosis (ABPA) is a severe complication in cystic fibrosis (CF), which is difficult to identify because of overlapping unspecific diagnostic features with common CF-manifestations. The cellular allergen stimulation test (CAST) is used in diagnosis of allergic and pseudoallergic reactions. This assay is based on the determination of sulfidoleukotrienes, which are produced by allergen-stimulated basophils in vitro. The potential role of CAST in diagnosis of ABPA was evaluated in this study. The CAST assay was applied in 27 CF-patients including eight subjects with positive clinical and serological signs of ABPA. Additional to the Nelson-criteria for diagnosis of ABPA specific IgE against recombinant Aspergillus antigens (rAsp f 1, 2, 3, 4, and 6) were assessed. The CAST results were positive in all ABPA-patients and in five controls without any sign of ABPA except positive specific IgE against Aspergillus fumigatus (sensitivity of 100%, specificity of 74%). Specific IgE against rAsp f 4 and/or f 6 were positive in six of the eight ABPA-patients, but not in the controls. Positive CAST results, total serum IgE > 500 U/ml and positive IgE antibodies against rAsp f 4 and/or f 6 were only found in ABPA-patients (specificity of 100%). The CAST assay on its own includes high sensitivity with lower specificity. For the discrimination of ABPA from sensitization to Aspergillus, the CAST, the highly elevated total serum IgE and rAsp in combination are potential auxiliary diagnostic parameters.