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Quantitative comparison of TB1 (A) and TB2 (B) IFN-γ levels in QuantiFERON-TB Gold Plus borderline tests. The area colored in gray corresponds to the equivocal range between 0.20 and 0.70 IU/ml. The dashed line indicates the standardized 0.35-IU/ml positivity cutoff. Regression lines for the NIL-subtracted antigen tubes are plotted. Abbreviations: IU, international units; CLIA, chemiluminescence immunoassay; ELISA, enzyme-linked immunosorbent assay.
