Performance of QuantiFERON-TB Gold test compared to tuberculin skin test in detecting talent tuberculosis infection in HUV-positive individuals in IRAN

ABSTRACT

There is limited data about the performance of QuantiFERON-TB Gold [QFT-G] test in detecting latent tuberculosis infection [LTBI] in our region. We intended to determine the performance of QFT-G compared to conventional tuberculin skin test [TST] in detecting LTBI in HIV-positive individuals in Iran. This study was conducted in a HIV clinic in Tehran, Iran in April 2007. A total of 50 consecutive HIV-positive patients, not currently affected with active tuberculosis [TB], were recruited; 43 [86%] were male. The mean age was 38 +/- 7.2 years [21-53]. All had history of Bacillus Calmetta Guerin [BCG] vaccination. A TST with purified protein derivative [PPD] and whole-blood interferon-gamma release assay [IGRA] in reaction, to ESAT-6 and CFP-10 antigens was performed and measured by enzyme-linked immune-sorbent assay [ELISA]. The agreement between TST and QFT=G results were analyzed using Kappa test. A total of 36 [72%] patients had negative TST. For QFT-G, 20 [40%] tested positive, 19 [38%] tested negative, and the results in 11 cases [22%] were indeterminate. A total of 14 [28%] patients had a CD4 count of < 200 .Of the 14, TST + group, 12 had QFT-G +, only one case TST +/QFT-G-, and QFT-G was indeterminate in one TST positive case. Of the 36 patients with negative TST test, 8 [22%] had positive GFT-G and 10 [28%] yielded indeterminate results. There was no association between a positive TST and receiving highly active anti-retroviral therapy [HAART] or CD4 counts was not significant [P=0.06]. Although TST results were not significantly different in patients with CD <200 vs. CD4>200 [P=0.095], association between QFT-G results and CD4 cutoff of 200 reached statistical significance [P= 0.027]. Agreement Kappa coefficient between TST and QFT-G was 0.54 [Kappa = 0.54, 95% CI = 38.4-69.6, P < 0.001]. Detecting LTBI in HIV-positive individuals showed moderate agreement between QFT-G and LTBI in our study. Interestingly, our findings revealed that nontuberculous mycobacteria and prior BCG vaccination have minimal influence on TST results in HIV patients in Iran