Median and mean IFN-γ measurements for QuantiFERON-TB Gold In-Tube tests performed on the same subjects in three labs.

Nil = IFN-γ concentrations (IU/mL) in plasma from the Nil tube of the QuantiFERON-TB Gold In-Tube test (QFT-GIT); TB = IFN-γ concentrations (IU/mL) in plasma from the TB tube of QFT-GIT; TB Response = TB minus Nil.*Includes 7 subjects with discordant QFT-GIT interpretations.†Concordant positive among results from all 3 labs.§Concordant negative among results from all 3 labs.