Comparison of QuantiFERON-TB Gold In-Tube and QuantiFERON-TB Gold-Plus in the Diagnosis of Mycobacterium tuberculosis Infections in Immunocompromised Patients: a Real-World Study

QuantiFERON-TB Gold Plus (QFT-Plus) is an emerging QuantiFERON test after QuantiFERON-TB Gold In-Tube (QFT-GIT) for tuberculosis infection detection; it is an IFN-gamma release assay. We compared QFTPlus, which has an additional TB antigen 2 (TB2) tube to induce cell-mediated (CD8(+) T cell) immune responses, with QFT-GIT. We conducted this study to assess the agreement of the QFT-GIT and QFT-Plus assays in immunocompromised patients in a clinical setting. A total of 278 immunocompromised patients and 175 immunocompetent patients from different departments were continuously enrolled from August 2020 to March 2021, and each patient underwent both tests. Correlations between QFT-GIT and QFT-Plus assays showed good agreement (kappa value = 0.859). Patients receiving long-term immunosuppressant therapy had the lowest concordance between QFT-GIT and QFT-Plus assays; 9 out of 11 positive latent tuberculosis infection (LTBI) cases were diagnosed by the QFT-Plus assay, implying that QFT-Plus may detect more LTBI than QFT-GIT does in these patients. Indeterminate results were associated with lower lymphocyte, CD4(+) T cell, and CD8(+) T cell absolute counts, and with lower CD4/CD8 ratios. In conclusion, we found that the QFT-GIT and QFT-Plus assays had high agreement not only in immunocompetent patients but also in immunocompromised patients. QFT-Plus may detect more LTBI than QFT-GIT in patients receiving long-term immunosuppressant therapy. Thresholds were established for lymphocyte absolute counts of >1.15 x 10(9) cells, and for CD4(+) T cell absolute counts of >467.7 x 10(6) to 478.5 x 10(6) cells, which may lessen the incidence of indeterminate results. IMPORTANCE This study evaluated the performance of QFT-GIT and QFT-Plus in the diagnosis of M. tuberculosis infection in immunocompromised patients and found that QFT-Plus may detect more LTBI than QFT-GIT does in patients receiving long-term immunosuppressant therapy. We believe that our study makes a significant contribution to the literature because it highlights the different diagnostic accuracies of QFT-GIT and QFT-Plus in different subpopulations of immunocompromised and immunocompetent patients. Selecting a test with better performance, particularly in patients with a high risk of developing active TB, may assist the health sector in better managing TB. Furthermore, we believe that this study will be of significance to the diagnosis of LTBI.