Performance of QuantiFERON-TB Gold test compared to tuberculin skin test in detecting latent tuberculosis infection in HIV- positive individuals in Iran

Background: 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. Methods: 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 Calmette 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 immuno-sorbent assay (ELISA). The agreement between TST and QFT-G results were analyzed using Kappa test. Results: A total of 36 (72) patients had negative and 14 (28) revealed positive 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 tests, 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 absolute CD4 counts. Similarly, the association between QFT-G results and receiving HAART or CD4 counts was not significant (P = 0.06). Although TST results were not significantly different in patients with CD4 200 vs. CD4 > 200 (P = 0.295), 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). Conclusion: 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.