Receiver operating characteristic curve analysis of four Aspergillus-specific IgG assays for the diagnosis of chronic pulmonary aspergillosis

Measurement of Aspergillus-specific IgG is central to the diagnosis of chronic pulmonary aspergillosis (CPA), but manufacturers' guidance on test interpretation is based on unpublished data. We performed the first receiver operating characteristic (ROC) area under the curve (AUC) analysis to identify optimal cut-offs for this test in relation to European controls. Aspergillus-specific IgG levels were measured in sera from British adults with CPA and European healthy controls by ImmunoCAP, Immulite, Serion and Bio-Rad assays. ROC AUC analysis was performed to identify optimal cut-offs. ROC AUC results were; Bio-Rad 0.955, Immulite 0.948, ImmunoCAP 0.956 and Serion 0.944. Optimal diagnostic cut-offs were 1.5 AU/mL for Bio-Rad (93% sensitive, 98% specific), 25 mg/L for Immulite (93% sensitive, 99% specific), 50 mg/L for ImmunoCAP (84% sensitive, 96% specific) and 50 U/mL for Serion (84% sensitive, 91% specific). These cut-offs differ from manufacturers' guidance and from those previously calculated in relation to Ugandan controls.