IFN-γ responses differed significantly in individuals who had CXR suspicious of active TB (344/416) vs. those who had a normal CXR (72/416), when measured using TSPOT.TB [58 (IQR: 15–153) vs. 31 (8–101) SFC⋅10−6 PBMCs; p<0.01] and QFT-GIT assays [1.1 (0.2–4.6) vs. 0.3 (0.0–2.3) IU⋅ml−1; p<0.01], but not in response to PPD [96 (28–180) vs. 92 (20–142) SFC⋅10−6 PBMCs; p = 0.37]. This evidence concerns the gene IFNG and tuberculosis.