This examination identifies whether an individual has been infected by the bacteria responsible for tuberculosis. There are two primary methods to test for TB infection: skin tests and blood tests. For the TB skin test, a small dose of tuberculin is injected under the skin. The individual then revisits their healthcare provider within 48 to 72 hours to check for a reaction at the site of the injection. This procedure is also called the tuberculin skin test or Mantoux test. A positive result indicates that the person has encountered TB bacteria at some point, but it does not confirm if the infection is active at present.The TB blood test, known as an interferon-gamma release assay, comes in two forms approved by the U.S. Food and Drug Administration (FDA) and available in the United States: the QuantiFERON®-TB Gold Plus (QFT-Plus) and the T-SPOT®.TB test (T-Spot). A positive result from these tests signifies previous infection with TB bacteria, but like the skin test, it does not determine if the infection is currently active.