The majority of people who are infected with MTB do not exhibit any clinical, radiological or bacteriological evidence of the pathogen and may remain asymptomatic and not infectious. These groups are considered to have latent tuberculosis infection (LTBI). It has been estimated that people with LTBI are at 5%-10% risk for developing active TB during their lifetime. The risk of progression from LTBI to active TB is higher in young children, people co-infected with human immunodeficiency virus (HIV), immunocompromised patients due to co-morbidity (e.g., diabetes, malignancy, renal disease) and/or long-term use of immunosuppressant medications (e.g., corticosteroids, tumor necrosis factor-alpha antagonists). Given that LTBI represents a global reservoir of potential TB epidemic, it is important to identify and, if appropriate, treat people with LTBI in order to reduce the risk of progression to active TB Unfortunately, there is no diagnostic gold standard for identification of individuals with LTBI who would potentially benefit from such prophylactic treatment (i.e., isoniazid) indicated for the prevention of active TB. Instead, the available screening tests for LTBI provide indirect assessment of the presence of LTBI by relying on a host s immunological response to TB antigens.