Latent TB infection (LTBI) is defined as a state of persistent immune response to stimulation by M. tuberculosis antigens without evidence of clinically manifested active TB. Current methods for LTBI detection are the tuberculin skin test (TST) and the interferon-gamma release assays (IGRAs). Both these tests indicate prior host immunosensitisation to M. tuberculosis antigens and do not provide information regarding viability of the organism within the host. Around 10 percent of immunocompetent adults with LTBI develop active TB in their lifetime: of these, approximately half (i.e. 5%) develop disease within 2 to 5 years of acquiring the infection. The risk of progression of LTBI to active TB disease is increased in HIV/AIDs, in very young children, and in persons with solid and haematological transplant, end-stage renal failure on haemodialysis, silicosis, head and neck malignancies, and diabetes. Isoniazid preventive therapy has been shown to reduce the risk of developing active TB by 60–90 percent. However, it is associated with a risk of hepatoxicity, which increases with age. It is recommended that LTBI testing be targeted at groups/persons with a high risk of progression to active disease (e.g. close contacts, those with HIV infection) and/or for whom the benefit of PT outweighs the risk of hepatotoxicity.