IFNG and rheumatoid arthritis: It is interesting that TB Ag-stimulated IFN-γ levels in QFT-G assay were all above 2.74 IU/ml in our RA-TB patients, similar to previous findings that 16 of 19 contacts with progression to TB had strong IFN-γ responses >3.5 IU/ml in QFT-G assay [14].