Importance of operational factors in the reproducibility of Aspergillus galactomannan enzyme immune assay.

BACKGROUND:The Platelia Aspergillus Ag assay (Bio-Rad) is designed for detecting Aspergillus galactomannan (GM) and is widely used for diagnosing invasive aspergillosis but is hampered by variable occurrences of unreproducible positive results. Frequency and origin of these unreproducible results have not been formally studied. METHODS:Different technicians simultaneously performed four tests on 550 consecutive sera from adult patients (Test#1-Test#2 for extraction#1 and Test#3-Test#4 for extraction#2). The samples were classified as confirmed negative [all tests with GM optical density index (GM-ODI) 0.4) upon retesting after storage ≤72h at 4 °C (n = 20) or eight months at -20 °C (n = 17). CONCLUSIONS:Operational unreproducible positives represent 33% of the GM-positive results and a second sample evaluation appears mandatory to avoid useless investigations or treatments. When operational artifacts are excluded, GM remains stable at standard storage conditions.