Diagnostic value of T-SPOT.TB interferon-γ release assays for active tuberculosis

The aim of the present study was to evaluate the diagnostic value of interferon-γ release assays for the detection of active tuberculosis (ATB) in patients previously vaccinated with Bacillus Calmette-Guérin (BCG). In total, 540 patients underwent the T-SPOT.TB test, including 295 patients with active pulmonary TB (PTB), 52 patients with active extrapulmonary TB (EPTB), 11 individuals with inactive TB and 182 non-TB cases. Simultaneously, 186 patients with ATB, including PTB and EPTB cases, and 125 non-TB patients underwent tuberculin skin tests (TST). Associations between the sensitivity of the T-SPOT.TB assays and lung lesion severity, positive smear grade, disease site and the duration of anti-TB treatment were evaluated. The sensitivity and specificity values of the T-SPOT.TB assay for diagnosing ATB were 76.66 and 76.37%, respectively, and the positive rate in the inactive TB test results was significantly lower (23.63%; P<0.001). The diagnostic sensitivity was higher in the PTB cases when compared with the EPTB cases (P=0.01). Furthermore, the diagnostic sensitivity of the ATB cases undergoing anti-TB treatment was significantly lower when compared with the cases not undergoing treatment (P=0.002), and the sensitivity gradually decreased with the treatment duration (P=0.01). In addition, a statistically significant difference was identified in the specificity between the T-SPOT.TB assay and the TST (76.37 vs. 51.15%; P<0.001), whereas the sensitivity values did not differ significantly (76.66 vs. 75.56%). Therefore, the results indicated that the T-SPOT.TB assay is a promising diagnostic test for active PTB in a BCG-vaccinated population, and should replace the TST. As the administration of anti-TB treatment resulted in a lower sensitivity to the diagnostic test, the T-SPOT.TB assay may also be suitable for the assessment of treatment outcomes.