Figure 1

The trend of proportion of positivity by QFTGIT against the skin test indurations. Whole blood samples were collected from study participants directly into tubes containing TB-specific antigens, mitogen and nil. The samples were incubated for 24 hours at 37°C, plasma was collected and IFNγ assay was performed using ELISA. The results were interpreted as positive, negative or indeterminate on the basis of the manufacturer's recommended cut-off value (IFN-γ ≥ 0.35 IU/ml) using QFTGIT analysis software developed by the company. Tuberculin skin test (TST) was also performed by administrating 0.1 ml (2T.U/0.1 ml) tuberculin PPD RT23 (Statens Serum Institute, Copenhagen, Denmark) intradermally in the middle of the left forearm. The diameter of the indurations was measured transversely after 48-72 h using a ball-point pen and flexible plastic ruler. The subjects were categorized in to three groups based on the size of skin test induration (0 mm, >0 < 10 mm and ≥ 10 mm) and the positivity by QFTGIT was compared for the three groups.