The three studies conducted in countries with a high TB incidence (India, South Africa) can only to a limited extent be compared with studies conducted in TB low incidence countries (Germany, USA), because they included only a small number of subjects with IGRA results close to the diagnostic threshold and had high overall rates of positive IGRA results of between 40% and 57% and large maximum individual variation ranges of the absolute IFN-γ response (8.41 to 11.11 IU/ml for the QFT) [20,21,43]. The gene discussed is IFNG; the disease is tuberculosis.