An Evaluation of the Performance of the IMMY Aspergillus Galactomannan Enzyme-Linked Immunosorbent Assay When Testing Serum To Aid in the Diagnosis of Invasive Aspergillosis

Abstract

The objectives of this study were to evaluate the performance of the recently released IMMY Aspergillus galactomannan enzyme immunoassay (IMMY GM-EIA) when testing serum samples and to identify the optimal galactomannan index (GMI) positivity threshold for the diagnosis of invasive aspergillosis (IA). This was a retrospective case/control study, comprising 175 serum samples obtained from 131 patients, 35 of whom had probable or possible invasive fungal disease (IFD) as categorized using recently revised, internationally accepted definitions. The IMMY GM-EIA was performed following the manufacturer's instructions. Performance parameters were determined and receiver operator characteristic analysis was used to identify an optimal GMI threshold. Concordance with the Bio-Rad Aspergillus Ag assay (Bio Rad GM-EIA) and IMMY sona Aspergillus lateral flow assay was assessed. The median GMIs generated by the IMMY GM-EIA for samples originating from probable IA/IFD cases (n = 31), possible IFD (n = 4), and control patients (n = 100) were 0.61, 0.11, and 0.14, respectively, and were comparable to those of the Bio-Rad GM-EIA (0.70, 0.04, and 0.04, respectively). Overall qualitative observed sample agreement between the IMMY GM-EIA and Bio-Rad GM-EIA was 94.7%, generating a kappa statistic of 0.820. At a GMI positivity threshold of ≥0.5, the IMMY GM-EIA had a sensitivity and specificity of 71% and 98%, respectively. Reducing the threshold to ≥0.27 generated sensitivity and specificity of 90% and 92%, respectively. The IMMY GM-EIA provides a comparable alternative to the Bio-Rad GM-EIA when testing serum samples. Further prospective, multicenter evaluations are required to confirm the optimal threshold and associated clinical performance.

Keywords: Aspergillus diagnostics; ELISA; galactomannan; invasive aspergillosis; serum.