Serologic diagnosis of allergic bronchopulmonary aspergillosis in patients with cystic fibrosis through the detection of immunoglobulin G to Aspergillus fumigatus.

Allergic bronchopulmonary aspergillosis (ABPA) is seen in approximately 10% of patients with cystic fibrosis (CF) and can be difficult to diagnose. Consensus criteria require the presence of multiple elevated immunologic markers such as total immunoglobulin E (IgE), Aspergillus IgE and Aspergillus IgG, or precipitins for a robust diagnosis. There is some degree of standardization of total IgE and Aspergillus IgE levels, but there is no standardization in the measurement of IgG antibodies or precipitins to Aspergillus. The interpretation of results may, therefore, be confusing. Eighty-seven patients with CF were categorized as having ABPA or as controls, using the consensus criteria and an in-house enzyme immunoassay to measure IgG levels to Aspergillus. All sera from patients were then analyzed by commercial fluorescent immunoassay (FEIA) for the quantitative detection of anti-Aspergillus IgG. FEIA results were analyzed against the consensus conference minimum diagnostic criteria to ascertain a cutoff point, which could predict a diagnosis of ABPA in CF. Eighty patients with CF and with no or incomplete evidence of ABPA had a mean FEIA score of 51.1 mg/L, whereas 7 CF patients with ABPA had a mean FEIA score of 132.5 mg/L. Using receiver operator characteristic curve analysis of the ImmunoCAP (Phadia) IgG score on ABPA versus all other patients gave an area under the curve of 0.933 (estimated SE, 0.027). This analysis provisionally suggested that a score of 90 mg/L may be used as a cutoff point, which would give a sensitivity of 91% and specificity of 88.0% for the diagnosis of ABPA, though this requires further validation. This quantitative approach to Aspergillus IgG measurement in patients with CF along with the results of other tests will hopefully provide a more accurate approach to the diagnosis of ABPA.