QuantiFERON-TB Gold PLUS versus QuantiFERON- TB Gold In-Tube test for diagnosing tuberculosis infection

BACKGROUND/AIMS: QuantiFERON-TB Gold PLUS (QFT-PLUS) was developed as a new version of the interferon-γ (IFN-γ) release assay that contains an extra antigen tube to elicit a CD8+ T-cell response in addition to a CD4+ T-cell response. This study aimed to evaluate the performances of QFT-PLUS versus QuantiFERON-TB Gold In-Tube (QFT-GIT) for detecting tuberculosis (TB) infection. METHODS: Between October, 2016 and May, 2018, 137 participants were prospectively recruited and subjected to QFT-GIT and QFT-PLUS testing. The concordance between tests and performance based on different immune states and/or TB infection risk were evaluated. RESULTS: The 137 participants were classified as follows: active TB (n = 14), TB contact (n = 14), screening before biologic therapy (n = 85) and other disease (n = 24). The positive results for either test were 100% (n = 14/14), 42.9% (n = 6/14), 15.3% (n = 13/85), and 62.5% (n = 15/24) in each four groups, respectively. The QFT-GIT and QFT-PLUS test results showed good concordance with 91.2% agreement and a Cohen's κ of 0.807. The good concordance between two tests was also observed in 64 immunocompromised subjects (agreement of 90.6% and a Cohen's κ of 0.711). The intra-class correlation coefficient for each antigen tube of the QFT-PLUS showed a good correlation with the IFN-γ release of the QFT-GIT (TB1 = 0.912, p < 0.001; TB2 = 0.918, p < 0.001). CONCLUSION: QFT-PLUS showed highly comparable results to those of QFT-GIT for diagnosing TB infection in South Korea as well as in immunocompromised subjects.