IFNG and tuberculosis: The QuantiFERON®-TB GOLD In-Tube assay (QFT-GIT, Cellestis Limited, Carnegie, Victoria, Australia) is a commercial IGRA that measures IFN-γ response as the difference in IFN-γ concentration when blood is incubated with TB antigen stimulation in a TB Antigen tube minus the concentration when incubated without antigen in the Nil tube.