Variability of the QuantiFERON®-TB gold in-tube test using automated and manual methods.
BACKGROUND
The QuantiFERON®-TB Gold In-Tube test (QFT-GIT) detects Mycobacterium tuberculosis (Mtb) infection by measuring release of interferon gamma (IFN-γ) when T-cells (in heparinized whole blood) are stimulated with specific Mtb antigens. The amount of IFN-γ 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-γ was measured in automated and manual ELISAs. Variability in interpretations and IFN-γ measurements was assessed between automated (A1 vs. A2) and manual (M1 vs. M2) ELISAs. Variability in IFN-γ 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 not uniform; within-subject variability was greater with higher IFN-γ measurements and with manual ELISAs. For subjects with mean TB Responses ±0.25 IU/mL of the 0.35 IU/mL cutoff, the within-subject standard deviation for two manual tests was 0.27 (CI95 = 0.22-0.37) IU/mL vs. 0.09 (CI95 = 0.07-0.12) IU/mL for two automated tests.


CONCLUSIONS
QFT-GIT ELISA automation may reduce variability near the test cutoff. Methodological differences should be considered when interpreting and using IFN-γ release assays (IGRAs).
Division of Tuberculosis Elimination, Centers for Disease Control and Prevention, Atlanta, Georgia, United States of America.
William C
WC
Whitworth
Epidemiology Services Branch, United States Air Force School of Aerospace Medicine, Brooks City-Base, Texas, United States of America.
Donald J
DJ
Goodwin
Epidemiology Services Branch, United States Air Force School of Aerospace Medicine, Brooks City-Base, Texas, United States of America.
Laura
L
Racster
Department of Occupational Medicine/TB Prevention/Deployment Medicine, Wilford Hall Medical Center, Reid Clinic, Lackland Air Force Base, Texas, United States of America.
Kevin B
KB
West
Division of Tuberculosis Elimination, Centers for Disease Control and Prevention, Atlanta, Georgia, United States of America ; Northrop Grumman Information Systems Sector, Atlanta, Georgia, United States of America.
Stella O
SO
Chuke
Division of Tuberculosis Elimination, Centers for Disease Control and Prevention, Atlanta, Georgia, United States of America ; CDC Foundation, Atlanta, Georgia, United States of America.
Laura J
LJ
Daniels
Division of Tuberculosis Elimination, Centers for Disease Control and Prevention, Atlanta, Georgia, United States of America ; Northrop Grumman Information Systems Sector, Atlanta, Georgia, United States of America.
Brandon H
BH
Campbell
Epidemiology Services Branch, United States Air Force School of Aerospace Medicine, Brooks City-Base, Texas, United States of America ; CDC Foundation, Atlanta, Georgia, United States of America.
Jamaria
J
Bohanon
Epidemiology Services Branch, United States Air Force School of Aerospace Medicine, Brooks City-Base, Texas, United States of America ; CDC Foundation, Atlanta, Georgia, United States of America.
Atheer T
AT
Jaffar
Professor Emeritus of Biostatistics, University of South Carolina, Columbia, South Carolina, United States of America.
Wanzer
W
Drane
Epidemiology Consult Services, United States Air Force School of Aerospace Medicine, Wright-Patterson Air Force Base, Dayton, Ohio, United States of America.
Paul A
PA
Sjoberg
Division of Tuberculosis Elimination, Centers for Disease Control and Prevention, Atlanta, Georgia, United States of America.
Gerald H
GH
Mazurek
D000328:Adult; D000942:Antigens, Bacterial / Q000276:immunology; D057205:Automation, Laboratory; D004797:Enzyme-Linked Immunosorbent Assay; D005260:Female; D006046:Gold; D006801:Humans; D007371:Interferon-gamma / Q000097:blood* / Q000378:metabolism; D059425:Interferon-gamma Release Tests / Q000379:methods*; D008297:Male; D008875:Middle Aged; D009169:Mycobacterium tuberculosis / Q000276:immunology / Q000472:pathogenicity*; D013601:T-Lymphocytes / Q000276:immunology; D014374:Tuberculin Test / Q000379:methods*; D014376:Tuberculosis / Q000097:blood / Q000175:diagnosis* / Q000276:immunology; D055815:Young Adult
D000942:Antigens, Bacterial; C072681:Mycobacterium tuberculosis antigens; D006046:Gold; D007371:Interferon-gamma