Comparison of interferon gamma-inducible protein-10 and interferon gamma-based QuantiFERON TB Gold assays with tuberculin skin test in HIV-infected subjects.

We aimed to compare the positivity of the QuantiFERON TB gold in-tube (QFT-IT antigens) specific interferon gamma (IFN-γ/QFT-IT) and IFN-γ-inducible protein-10 (IP-10/QFT-IT) assays with tuberculin skin test (TST) among human immunodeficiency virus (HIV)-infected individuals in a TB endemic setting. A total of 180 HIV-infected subjects, with no evidence of active TB, were recruited. IFN-γ and IP-10 levels specific to QFT-IT antigens were measured in plasma from QFT-IT tubes. The overall positivity of TST at the 5-mm cut-off point (19%) was significantly lower when compared to IFN-γ/QFT-IT (38%) and IP-10/QFT-IT (45%) assays. The positivity of IP-10/QFT-IT was significantly higher than that of IFN-γ/QFT-IT (P = 0.038). Indeterminate results for IFN-γ/QFT-IT and IP-10/QFT-IT were more frequent in subjects with CD4 count <100 cells/μL than in those with >100 cells/μL. IFN-γ/QFT-IT (9%) yielded significantly higher number of indeterminate results than IP-10/QFT-IT (5%). The frequency of these responses is higher than the proportion of individuals with positive TST results. However, 6 IFN-γ/QFT-IT- or IP-10/QFT-IT-negative subjects were positive for TST at the 5-mm cut-off point. Prospective and prognostic studies are required to clarify the significance of these data.