Title:Performance of the IMMY® and OLM® lateral flow assays for Aspergillus galactomannan compared to fungal culture and Platelia™ galactomannan enzyme immuno-assay

Author:Wendy P McKinney, Bronwyn Findon, Chris Mansell, Sally A Roberts and Arthur J Morris

Abstract:Objectives: To investigate the performance of two lateral flow assays (LFAs) detecting Aspergillus antigens, galactomannan (GM) or glycoprotein antigen, compared with Aspergillus culture and GM enzyme immunoassay (EIA) results.
Methods: Lower respiratory tract samples, either bronchoalveolar lavage or bronchial wash specimens, were tested with the Platelia™ GM EIA, IMMY® LFA, or OLM® LFA. Test results were compared to culture and for both LFAs compared to the GM EIA. Three cut-off indexes were used for the GM EIA, ≥0.5, ≥1.0 and ≥1.5. Two optical density (OD) cut-offs were used for the IMMY LFA ≥0.5 and ≥1. OD readers were used to interpret both LFAs. Positive and negative predictive values (PPV, NPV) were calculated for clinically encountered prevalence rates of 5%, 10% and 15%.
Results: The sensitivity of the GM EIA for a positive Aspergillus culture was unaltered by the OD value used to define a positive. For Aspergillus culture the specificity, PPVs, test concordance and diagnostic odds ratio all increased with increasing GM EIA index cut-off values from ≥0.5 to ≥1.5. The OLM LFA and the IMMY LFA with the 1.0 OD cut-off had similar performance values for positive Aspergillus culture results. Both LFA assays had NPVs of 89%-97% vs. 94%-98% for GM EIA. Most specimens with either a positive GM EIA or LFA and a negative Aspergillus culture result were either culture negative, 29-60%, or for GM EIA and OLM LFA grew yeasts, 22 -73%, not known to have cross-reacting antigens.
Conclusions: Both LFAs are user friendly. The test performance of the IMMY LFA is improved when an OD of ≥1 is used to define a positive and at this cut-off the results of both LFAs are comparable. Positive assays with negative Aspergillus cultures are not due to the presence of cross-reacting fungi. Both LFAs had high NPVs which help rule out invasive aspergillosis.
Keywords: Aspergillosis, Aspergillus, lateral flow assay, enzyme-immunoassay, fungal diagnosis, point-of-care assays.
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