Variability of the QuantiFERONH-TB Gold In-Tube Test Using Automated and Manual Methods

Background: The QuantiFERONH-TB Gold In-Tube test (QFT-GIT) detects Mycobacterium tuberculosis (Mtb) infection by measuring release of interferon gamma (IFN-c) when T-cells (in heparinized whole blood) are stimulated with specific Mtb antigens. The amount of IFN-c is determined by enzyme-linked immunosorbent assay (ELISA). Automation of the ELISA method may reduce variability. To assess the impact of ELISA automation, we compared QFT-GIT results and variability when ELISAs were performed manually and with automation. Methods: Blood was collected into two sets of QFT-GIT tubes and processed at the same time. For each set, IFN-c was measured in automated and manual ELISAs. Variability in interpretations and IFN-c measurements was assessed between automated (A1 vs. A2) and manual (M1 vs. M2) ELISAs. Variability in IFN-c measurements was also assessed on separate groups stratified by the mean of the four ELISAs. Results: Subjects (N = 146) had two automated and two manual ELISAs completed. Overall, interpretations were discordant for 16 (11%) subjects. Excluding one subject with indeterminate results, 7 (4.8%) subjects had discordant automated interpretations and 10 (6.9%) subjects had discordant manual interpretations (p = 0.17). Quantitative variability was no