Interferon-Gamma Release Assay Performance in Pulmonary and Extrapulmonary Tuberculosis

Background: The diagnosis of tuberculosis remains difficult. This study aimed to assess performance of interferon-gamma release assay (IGRA) in diagnosis of active tuberculosis (ATB) with pulmonary and extrapulmonary involvements, and to determine the diagnostic role of IGRA (T-SPOT.TB) and tuberculin skin test (TST) in BCG-vaccinated population. Methods and Findings: Two hundred twenty-six ATB suspects were recruited and examined with T-SPOT.TB. Among them, fifty-two and seventy-six subjects were simultaneously tested by TST with 5TU or 1TU of purified protein derivative (PPD). The sensitivity of T-SPOT.TB was 94.7 % (71/75), comparable in pulmonary and extrapulmonary disease groups (95.6 % vs. 93.3%, P.0.05), while the specificity was 84.10 % (90/107) but differed in two groups (69.2 % vs. 88.9%, P = 0.02). Compared to T-SPOT.TB, TST with 5TU-PPD showed less sensitivity (92.3 % vs. 56.4%) and specificity (84.6 % vs. 61.5%) (both P,0.01); the sensitivity of TST with 1TU-PPD was 27.8%, and despite its specificity identical to T-SPOT.TB (both 82.8%) positive predictive value (PPV) was only 33.3%. By combining T-SPOT.TB with TST (1TU), the specificity rose to 95%, but the PPV stayed unchanged. Conclusions: IGRA could function as a powerful immunodiagnostic test to explore pulmonary and extrapulmonary TB, whil