Optimizing diagnostic approaches for allergic bronchopulmonary aspergillosis: Comparative analysis of IgG/IgE ELISA and serum precipitins assays.

Background: Allergic bronchopulmonary aspergillosis (ABPA) is a chronic lung condition that results from an overexuberant immune response, primarily to Aspergillus fumigatus. Diagnostic criteria have varied over time but current consensus requires elevated total immunoglobulin E (IgE) levels, A. fumigatus-specific IgE, and at least two of three of IgG response to A. fumigatus, elevated eosinophil levels, and imaging changes consistent with ABPA. The differentiation of asthma with A. fumigatus sensitization and ABPA remains controversial. Objective: To examine the results from a referral laboratory that provided analysis of specific antibody response to A. fumigatus via three assays: IgG index, IgE index, and IgG precipitins. The first two are measured by using an enzyme-linked immunosorbent assay (ELISA). Methods: Testing done for 539 consecutive patients evaluated for possible ABPA was analyzed. Results: Only 58 samples were positive for both IgG and IgE indexes, thereby meeting stringent serologic criteria for a diagnosis of ABPA. Only one third of the patients with a positive IgG index result also had positive precipitins results. Overall, the percentage of positive test results increased with age. Finally, the distribution of both A. fumigatus-specific IgG and IgE levels were approximately normal, not bimodal, which provides evidence that ABPA may exist on a spectrum with asthma with fungal sensitization. Conclusion: In this cohort, evidence of both an IgG and an IgE response to A. fumigatus was only seen in ∼10% of the samples, which indicated that ABPA is only found in a minority of patients in whom it is considered. ELISA is more sensitive than precipitins for identification of an overexuberant IgG response.