Interferon-Gamma Assay T-SPOT.TB in the Diagnostics of Latent Tuberculosis Infection

Introduction: Diagnostics of latent tuberculosis infection (LTBI) has been based on a century-old tuberculin skin test (TST). However, a positive reaction can result not only from infection with Mycobacterium tuberculosis, but also from BCG vaccination or cross-reaction with nontuberculous mycobacteria. T-SPOT.TB assay is a new test to diagnose tuberculosis infection by measuring in vitro T-cell interferon-gamma release in response to two Mycobacterium tuberculosis-specific antigens: ESAT-6 and CFP-10. Material and methods: T-SPOT.TB assay was performed on samples of whole blood (n = 137) from March to September 2010. Tuberculin skin test was carried out in 96 participants. A positive TST result was considered to be an induration of 10 mm or more. Results: Of the 137 patients tested, T-SPOT.TB assay results were positive in 37 (27%), negative in 98 (71.5%) and indeterminate in only 2 (1.5%) persons. We analyzed T-SPOT.TB and TST results in 96 patients who were subjected to both tests. Concordance between T-SPOT.TB and TST results (a 10-mm skin reaction interpreted as positive) was 79%. Fifteen (15.6%) patients had a positive TST result and a negative T-SPOT.TB, and 5 (5.2%) patients had a negative TST result and a positive T-SPOT.TB. We observed a good correlation between positive T-SPOT.TB results and the diameter of induration of ≥15 mm in TST results. Conclusions: T-SPOT.TB offers a more accurate approach than TST in the identification of tuberculosis infection. The study showed that the test T-SPOT.TB is a good diagnostic tool in identifying persons with tuberculosis infection. For a full confirmation of this assessment, it is necessary to examine more cases.