Tuberculin skin test or interferon gamma release assay - How to detect latent tuberculosis infection in sarcoidosis patients?

Introduction: Tuberculin skin test (TST) is one of the test recommended in initial evaluation of patients suspected for sarcoidosis and most patients have negative TST results. At present, an alterative to TST are the tests based on the measurement of interferon gamma release by sensitized T lymphocytes in response to stimulation by antigens specific for M.tuberculosis (IGRAs). In many countries IGRAs replaced TST for detection of the latent tuberculosis infection (LTBI). The role of IGRAs in sarcoidosis patients is still unknown. Object and rationale: The aim of this study was a head to head comparison between TST and one of IGRAs – Quantiferon TB Gold in Tube (QFT) and to determine which of them is better to detect LTBI in sarcoidosis patients. Material and method: 151 patients, mean age 38.3±10.3, treatment naive, with newly diagnosed pulmonary sarcoidosis were included in the study. According to the Polish recommendation, TST ≥10 mm was considered positive. Concordance between TST and QFT was assess using kappa (κ) coefficient. Results: TST was positive in 16/151 (10.5%) and QFT was positive in 7/151 (4.6%). There was no concordance between TST and QFT (κ -0.07). All sarcoidosis patients with positive TST had negative QFT. All of QFT positive had negative TST. Conclusion: Positive IGRAs among TST negative patients indicate, that skin reactivity to tuberculin is not parallel to ex vivo peripheral blood lymphocytes response to mycobacterial antigens. QFT is better than TST for detection of LTBI in sarcoidosis patients. Positive TST results in sarcoidosis patients are not connected with LTBI, as assessed by QFT.