IFNG and tuberculosis: So far, the published studies on IGRA serial testing and on the within-subject variability of the IFN-γ response among HCWs in countries with a low or intermediate incidence of TB demonstrate convincingly that subjects with a QFT result in a borderline zone between 0.2 to 0.7 IU/ml are significantly more likely to show an inconsistent result on retesting [37-40,42,44].