Therefore, increasing the accuracy and stability and then improving the rate of negative conversion from positive IGRA results are very important. Currently, new generation of QuantiFERON-TB Gold Plus includes two tubes for CD4 and CD8 T cells response, which can indicate TB immune response more specifically. The investigators applied this project to compare the performance of diagnosing LTBI by QuantiFERON-TB Gold Plus in comparing QuantiFERON-TB Gold In-tube.