PLoS One

BackgroundThe QuantiFERON\uc2\uae-TB Gold In-Tube test (QFT-GIT) detects Mycobacterium tuberculosis (Mtb) infection by measuring release of interferon gamma (IFN-\uce\ub3) when T-cells (in heparinized whole blood) are stimulated with specific Mtb antigens. The amount of IFN-\uce\ub3 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.MethodsBlood was collected into two sets of QFT-GIT tubes and processed at the same time. For each set, IFN-\uce\ub3 was measured in automated and manual ELISAs. Variability in interpretations and IFN-\uce\ub3 measurements was assessed between automated (A1 vs. A2) and manual (M1 vs. M2) ELISAs. Variability in IFN-\uce\ub3 measurements was also assessed on separate groups stratified by the mean of the four ELISAs.ResultsSubjects (N\ue2\u20ac\u160=\ue2\u20ac\u160146) 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\ue2\u20ac\u160=\ue2\u20ac\u1600.17). Quantitative variability was not uniform; within-subject variability was greater with higher IFN-\uce\ub3 measurements and with manual ELISAs. For subjects with mean TB Responses \uc2\ub10.25 IU/mL of the 0.35 IU/mL cutoff, the within-subject standard deviation for two manual tests was 0.27 (CI95\ue2\u20ac\u160=\ue2\u20ac\u1600.22\ue2\u20ac\u201c0.37) IU/mL vs. 0.09 (CI95\ue2\u20ac\u160=\ue2\u20ac\u1600.07\ue2\u20ac\u201c0.12) IU/mL for two automated tests.ConclusionQFT-GIT ELISA automation may reduce variability near the test cutoff. Methodological differences should be considered when interpreting and using IFN-\uce\ub3 release assays (IGRAs)