Until recently, the tuberculin skin test (TST) has been the only assay used for detecting latent tuberculosis infection (LTBI), but two ex-vivo tests, used as alternative methods to TST, based on enumerating the M. tuberculosis-specific interferon (IFN)-g response are now commercially licensed. The aim of this study was to compare the sensitivity and specificity of TST, QuantiFERON Gold (QFT-G), and T-SPOT.TB in diagnosing LTBI and active tuberculosis (TB). Materials and methods: This study was carried out with 95 participants including 3 groups (negative control, close contact, and patient groups) during a 10-month period from March 2007 to January 2008. Results: When the cut-off value of the TST was regarded as >=15 mm, 46.4% of the patients and 14.3% of the control group were found to have positive values. The sensitivity (51.4%) and the negative predictive value (NPV) (52.6%) of TST were lower than the specificity (83.3%) and the positive predictive values (PPV) (82.6%). The sensitivity and the PPV of the QFT-G test (78.4% and 76.3%, respectively) were higher than the specificity (62.5%) and NPV (65.2%). The PPV (81.8%) of the T- SPOT.TB test was higher than sensitivity (73.0%), specificity (75.0%), and NPV (64.3%). Conclusion: IFN-g tests could be useful in diagnosing LTBI and chemo-prophylaxis, as the false negativity of the TST was higher compared to both QFT-G and T-SPOT.TB. However, additional studies are needed to assess better the utility of these tests with large populations.

Until recently, the tuberculin skin test (TST) has been the only assay used for detecting latent tuberculosis infection (LTBI), but two ex-vivo tests, used as alternative methods to TST, based on enumerating the M. tuberculosis-specific interferon (IFN)-g response are now commercially licensed. The aim of this study was to compare the sensitivity and specificity of TST, QuantiFERON Gold (QFT-G), and T-SPOT.TB in diagnosing LTBI and active tuberculosis (TB). Materials and methods: This study was carried out with 95 participants including 3 groups (negative control, close contact, and patient groups) during a 10-month period from March 2007 to January 2008. Results: When the cut-off value of the TST was regarded as >=15 mm, 46.4% of the patients and 14.3% of the control group were found to have positive values. The sensitivity (51.4%) and the negative predictive value (NPV) (52.6%) of TST were lower than the specificity (83.3%) and the positive predictive values (PPV) (82.6%). The sensitivity and the PPV of the QFT-G test (78.4% and 76.3%, respectively) were higher than the specificity (62.5%) and NPV (65.2%). The PPV (81.8%) of the T- SPOT.TB test was higher than sensitivity (73.0%), specificity (75.0%), and NPV (64.3%). Conclusion: IFN-g tests could be useful in diagnosing LTBI and chemo-prophylaxis, as the false negativity of the TST was higher compared to both QFT-G and T-SPOT.TB. However, additional studies are needed to assess better the utility of these tests with large populations.