A significant correlation between the serum albumin concentration and the difference in ODI value on retesting was also recently reported.
A larger reduction in indices was observed on retesting sera with increasing albumin concentrations (11).
The storage conditions of specimens appear to have an impact on reproducibility, with a significant decline in the sample ODI reported after storage at −80°C (11).
An IA diagnosis also appears to be important, with nonreproducibility observed more frequently for retesting of false-positive samples from patients without IA (11, 12).
In stage i, Bland-Altman analysis demonstrated a reduced variance between optical density index (ODI) values for samples processed on two DS2 platforms (mean difference, −0.02; limits of agreement [LOA], −0.19 to 0.14) compared with the variance between samples processed manually and on a DS2 platform (mean difference, 0.02; LOA, −0.25 to 0.3).
In stage ii, 100% (14/14 samples) qualitative agreement was observed for serum samples from patients with IA, with no significant change in the ODI values when samples were processed on the DS2 platform.
While storage and disease status have been shown to affect the reproducibility of GM-EIA, other factors, such as human error, environmental contamination at the point of testing, and variability in local testing conditions between laboratories, may also have impacts on the assay's performance and reproducibility.
The present study aimed to evaluate the automation of the GM-EIA on an alternative open platform, the DS2 (Dynex Technologies) ELISA processing system, to test the impact of the DS2 system in reducing test variability.Although initially the GM-EIA reproducibility was reported to be excellent between laboratories (8), recent reports documented a lack of reproducibility for repeat testing of positive samples (9, 10).In particular, samples with an optical density index (ODI) at or around the positivity threshold (≅0.5) of the assay were regularly found to be negative on repeat testing (8, 11).A significant decrease in ODI values was observed for control serum samples on the DS2 platform (difference, 0.01; = 0.042).In stage iii, a significant reduction in the frequency of equivocal results, from 5.56% (136/2,443 samples) to 1.56% (15/961 samples), was observed after DS2 automation (difference, 4.0%; 95% confidence interval [CI], 2.7 to 5.2%; galactomannan antigen sandwich enzyme immunoassay (GM-EIA) is widely used as a screening method for prospective surveillance of invasive aspergillosis (IA) in patients at high risk of disease.
Samples were assigned to a case/control definition prior to retesting on the DS2 system.