There are two kinds of tests that can be used to help detect TB infection - the TB skin test (TST) and TB blood tests or Interferon-Gamma Release Assays (IGRAS) (i.e., QuantiFERON®-TB Gold test (QFT-G), QuantiFERON®-TB Gold In-Tube test (GFT-GIT) and T-SPOT®.TB test).
IGRAS and TSTs should be used as an aid in diagnosing infection with M. tuberculosis. A positive test result suggests that M. tuberculosis infection is likely; a negative result suggests that infection is unlikely. For IGRA test results either an indeterminate or borderline test result (T-SPOT® only) indicates an uncertain likelihood of M. tuberculosis infection.
A diagnosis of Latent Tuberculosis Infection (LTBI) requires that TB disease be excluded by medical evaluation. This should include checking for signs and symptoms suggestive of TB disease, a chest x-ray, and, when indicated, examination of sputum or other clinical samples for the presence of M. tuberculosis. Decisions about a diagnosis of M. tuberculosis infection should also include epidemiological and the patient’s medical history.