Usefulness of Tuberculin Skin Test and Three Interferon-Gamma Release Assays for the Differential Diagnosis of Pulmonary Tuberculosis

BACKGROUND: We compared the usefulness of tuberculin skin test (TST) and three interferon-gamma release assays (IGRAs) [QuantiFERON-TB Gold (QFT-2G), QuantiFERON-TB Gold In-tube (QFT-3G), T-SPOT.TB] as the supportive method for diagnosing pulmonary tuberculosis (TB). METHODS: The subjects were 66 patients who required clinical differentiation of pulmonary TB. The final clinical diagnosis of pulmonary TB in 22 patients and non-pulmonary TB in 44 patients was established by clinical specimens. RESULTS: In 22 patients with pulmonary TB, the positive response rate was 59.1% on TST, 81.8% on QFT-2G, 86.4% on QFT-3G and 95.5% on T-SPOT.TB. In 44 patients with non-pulmonary TB disease, the positive response rate was 40.9% on TST, 6.8% on QFT-2G, 6.8% on QFT-3G, 13.6% on T-SPOT.TB. Indeterminate results on three IGRAs were recognized in one patient each on QFT-2G and QFT-3G among patients with pulmonary TB and in two patients each on QFT-2G and QFT-3G among patients with non-pulmonary TB. However, there were no indeterminate results on T-SPOT.TB in either patient group. Patients with false-negative or indeterminate results on IGRAs had severe underlying diseases or were receiving immunosuppressive treatments. CONCLUSION: There were no significant differences among the three IGRA tests in this study. However, because the three IGRA tests showed a significantly higher positive response rate for patients with pulmonary TB and a lower positive response rate for patients with non-pulmonary TB than TST, the three IGRA tests seemed to be more useful than TST for the differentiation of patients with pulmonary TB.