Evaluation of a Quantitative Serological Assay for Diagnosing Chronic Pulmonary Aspergillosis

Abstract

The purpose of this study was to evaluate the clinical utility of a quantitative Aspergillus IgG assay for diagnosing chronic pulmonary aspergillosis. We examined Aspergillus-specific IgG levels in patients who met the following criteria: (i) chronic (duration of >3 months) pulmonary or systemic symptoms, (ii) radiological evidence of a progressive (over months or years) pulmonary lesion with surrounding inflammation, and (iii) no major discernible immunocompromising factors. Anti-Aspergillus IgG serum levels were retrospectively analyzed according to defined classifications. Mean Aspergillus IgG levels were significantly higher in the proven group than those in the possible and control groups (P < 0.01). Receiver operating characteristic curve analysis revealed that the Aspergillus IgG cutoff value for diagnosing proven cases was 50 mg of antigen-specific antibodies/liter (area under the curve, 0.94; sensitivity, 0.98; specificity, 0.84). The sensitivity and specificity for diagnosing proven cases using this cutoff were 0.77 and 0.78, respectively. The positive rates of Aspergillus IgG in the proven and possible groups were 97.9% and 39.2%, respectively, whereas that of the control group was 6.6%. The quantitative Aspergillus IgG assay offers reliable sensitivity and specificity for diagnosing chronic pulmonary aspergillosis and may be an alternative to the conventional precipitin test.

FIG 1

Average Aspergillus IgG level in serum from each group measured by fluorescent immunoenzyme assay. Data represent the means ± standard deviations (SDs). *, P value of <0.01.

FIG 2

ROC analysis for diagnosing probable and proven cases. The optimal cutoff value of Aspergillus IgG for diagnosing proven and probable cases was 50 mg_A/liter (AUC, 0.94; 95% confidence interval, 0.912 to 0.972; sensitivity, 0.98; specificity, 0.84).

FIG 3

The comparison of anti-Aspergillus precipitin (IgG) with specific Aspergillus IgG levels. Specific IgG was significantly higher in precipitin-positive patients; however, there were some positive cases with low Aspergillus IgG levels.