The median (IQR) IFN-γ levels (n = 149) were significantly higher in definite TB than non-TB pleural effusions (198.7 pg/ml [93.4 to 298.2] versus 0.0 pg/ml [0.0 to 0.0], P < 0.0001) (Fig. 2A). This evidence concerns the gene IFNG and tuberculosis.