Diagnostic specificity of a sandwich ELISA for Aspergillus-related diseases

A sandwich ELISA with specificity for a major antigen (Ag 7) of Aspergillus fumigatus has been compared with indirect ELISAs with use of crude antigenic (culture filtrate) extracts and found to have a sensitivity of 100% and specificity of 92.3% for antibody detection in sera of patients with allergic bronchopulmonary aspergillosis (ABPA) and aspergilloma. In the Ag 7 ELISA, all sera from groups with ABPA (21) and aspergilloma (15) had positive titers, and mean values for both these groups were significantly higher (p less than 0.001) than control levels. By comparison, in the indirect ELISAs, most sera of patients with ABPA were positive; the sensitivity was 81% to 90%, and the specificity was 87%. Sera from other disease groups including sera from 13 patients with farmer's lung, 16 with tuberculosis, and 10 individuals with positive prick test to either A. fumigatus or Alternaria alternata were also tested by both types of assay. Up to five of these sera elicited significant positive results in the indirect ELISA, and although two sera were also positive in the Ag 7-specific ELISA, these latter titers were both below the range of values for the sera from patients with ABPA. With the use of an IgG calibration curve, the sensitivity of the assay was determined as within the range of 1 to 10 microgram of specific IgG antibody per milliliter. The Ag 7-specific ELISA is therefore a highly specific, sensitive assay for antibody detection in Aspergillus-related diseases.