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.