IFNG and tuberculosis: Hence, in view of the available data on the within-subject variability of the IFN-γ response and the use of IGRAs in the serial testing of HCWs in countries with low and intermediate incidences of TB, we recommend using a borderline zone from 0.2 to 0.7 IU/ml for the interpretation of repeat QFT results in routine screening of HCWs with an increased LTBI risk (Figure 2).