• James D Mancuso, Gerald H Mazurek, David Tribble, Cara Olsen, Naomi E Aronson, Lawrence Geiter, Donald Goodwin, and Lisa W Keep.
• Division of Preventive Medicine, Walter Reed Army Institute of Research, Silver Spring, MD 20910, USA. james.mancuso@us.army.mil
• Am. J. Respir. Crit. Care Med.. 2012 Feb 15;185(4):427-34.

RationaleThere is uncertainty regarding how to interpret discordance between tests for latent tuberculosis infection.ObjectivesThe objective of this study was to assess discordance between commercially available tests for latent tuberculosis in a low-prevalence population, including the impact of nontuberculous mycobacteria.MethodsThis was a cross-sectional comparison study among 2,017 military recruits at Fort Jackson, South Carolina, from April to June 2009. Several tests were performed simultaneously with a risk factor questionnaire, including (1) QuantiFERON-TB Gold In-Tube test, (2) T-SPOT.TB test, (3) tuberculin skin test, and (4) Battey skin test using purified protein derivative from the Battey bacillus.Measurements And Main ResultsIn this low-prevalence population, the specificities of the three commercially available diagnostic tests were not significantly different. Of the 88 subjects with a positive test, only 10 (11.4%) were positive to all three tests; 20 (22.7%) were positive to at least two tests. Bacille Calmette-Guérin vaccination, tuberculosis prevalence in country of birth, and Battey skin test reaction size were associated with tuberculin skin test-positive, IFN-γ release assay-negative test discordance. Increasing agreement between the three tests was associated with epidemiologic criteria indicating risk of infection and with quantitative test results.ConclusionsFor most positive results the three tests identified different people, suggesting that in low-prevalence populations most discordant results are caused by false-positives. False-positive tuberculin skin test reactions associated with reactivity to nontuberculous mycobacteria and bacille Calmette-Guérin vaccination may account for a proportion of test discordance observed.

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