Comparison of aspergillus precipitin with quantitative aspergillus IgG assay

Background: Detection of IgG antibodies to Aspergillus fumigatus is important for diagnosing chronic pulmonary aspergillosis (CPA). Immunodiffusion assay has been widely used for detecting circulating anti- Aspergillus antibodies (precipitin), however, it appears to lack sensitivity. Recently, quantitative measurement of IgG to Aspergillus by using fluorescent immunoenzyme assay (ImmunoCap TM ) is commercially available. In this study, we examined performance of ImmunoCap TM with respect to diagnosis of CPA. Method: We detected serum Aspergillus precipitin in patients with following condition; 1) complaining subacute to chronic respiratory and/or systemic symptom, 2) developing radiological shadow in lung (cavitation, infiltration and thickness of pleura) within 3-6 months, and 3) existence of underlying chronic respiratory disease. These patients were divided to four groups (proven, probable, possible and control) according to classification criteria. We also examined specific IgG to Aspergillus for these collected sera by ImmunoCap TM . Result: From January 2007 to August 2013, 353 patients were studied. Aspergillus IgG values was significantly higher in the proven and probable groups than in the possible and control groups (p <0.01). ROC analysis revealed that cut off value of ImmunoCap TM for diagnosis of proven and probable cases was 50 mg A /L (AUC, 0.83; 95% CI, 0.786-0.874; sensitivity, 0.79; specificity, 0.74 ). Conclusions: The sensitivity and specificity of ImmunoCap TM for diagnosis of CPA were reliable. Thus, ImmunoCap TM may alternate with conventional precipitin test for diagnosing CPA. In addition, the quantitation of IgG might be useful for monitoring marker of antifungal treatment response.