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. 2019 Jan 21;69(10):1724–1730. doi: 10.1093/cid/ciz034

Figure 3.

Figure 3.

ESAT-6–free IGRA diagnostic accuracy in healthy South African adolescents. Blood was collected from QFT-negative (n = 117, open symbols) and QFT-positive (n = 83, filled symbols) healthy South African adolescents (cohort 3) in QFT and ESAT-6–free IGRA (E6FI) tubes and stimulated for 16–20 hours at 37°C; the IFN-γ concentration was measured by QFT enzyme-linked immunosorbent assay. A, Distribution of IFN-γ values measured by QFT and E6FI in all participants. The dotted line denotes QFT cutoff. B, Paired analysis (Wilcoxon matched-pairs signed rank test) of IFN-γ values measured by QFT and E6FI (TB Ag – Nil) in QFT-negative and QFT-positive adolescents. C, Correlation between IFN-γ values obtained by QFT and E6FI in all participants was assessed using the Spearman test. The dotted lines denote assay cutoffs: 0.35 IU/mL for QFT (vertical line) and 0.61 IU/mL for E6FI (horizontal line). Abbreviations: Ag, antigen; ESAT-6, early secretory antigenic target; IFN-γ, interferon-gamma; IGRA, interferon-gamma release assay; QFT, QuantiFERON-TB Gold In-tube; TB, tuberculosis.