Tuberculin skin test and QuantiFERON-TB Gold In-tube Test for latent tuberculosis in Thai HIV-infected adults

Background and objectiveLimited data exist for the performance of QuantiFERON-TB Gold In-tube Test (QFT-IT) in comparison to tuberculin skin test (TST) for detecting latent tuberculosis (LTB) in patients with human immunodeficiency virus (HIV) infection from tuberculosis (TB)-endemic Asia-Pacific countries. MethodsA cohort study of Thai HIV-infected patients without history of TB or LTB treatment was conducted from March 2012 through March 2013. Each patient underwent simultaneous TST and QFT-IT. ResultsAmong the 150 enrolled subjects, the median age was 40 years (range 17-65), 53% were male, and the median CD4 count was 367cells/L (range 8-1290). Reactive TST and positive QFT-IT were 16% and 13%, respectively, with low concordance between tests (kappa=0.26); correlation between TST reaction size and level of interferon- was moderate (r=0.34). Independent factors associated with discordant results were long-term smoking (adjusted odds ratio (aOR) 5.74; P=0.002) for TST-reactive, QFT-IT-negative subjects, and age greater than 52 years (aOR 5.56; P=0.02) and female gender (aOR 4.40; P=0.04) for TST non-reactive, QFT-IT-positive subjects. The level of agreement between both tests improved when using a TST cut-off of 10mm (kappa=0.39). ConclusionsIn our setting where QFT-IT is available but has limited use due to cost, TST with a cut-off of 10mm for reactivity should be the initial LTB test. HIV-infected women and persons older than 52 years with non-reactive TST and long-term smokers with reactive TST may benefit from subsequent QFT-IT. Tuberculin skin test (TST) remains the diagnostic test for latent tuberculosis in interferon-gamma release assay (IGRA)-unavailable HIV care settings, but the cut-off for reactivity needs to be adjusted accordingly. Women and patients older than 52 years with non-reactive TST and long-term smokers with reactive TST should undergo additional IGRA testing.