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The comprehensive evaluation of latent tuberculosis infection in health care workers and of patients with active tuberculosis using TST, ELISA, and ELISPOT methods

Aim: 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)-γ 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-γ 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.