A latent tuberculosis infection (LTBI) is detected by a positive blood test (e.g. IGRA: interferon-gamma release assay) or a skin test (e.g. THT/TST: tuberculin skin test), whereby an active tuberculosis disease is excluded at the same time. However, these tests cannot predict whether the infection will later develop into a disease or is already present. They should therefore be carried out primarily on people who are at particularly high risk of such a development (medically: progression). There is a particularly high risk in people who have recently been in contact with a person with infectious tuberculosis. In this case, the LTBI test becomes positive 8 to 12 weeks after contact. People with chronic immunodeficiency diseases (e.g. HIV) or those taking immunomodulating drugs (e.g. TNF-alpha antibody therapy) also have a higher risk of developing tuberculosis and should be tested. However, a positive result in people with no known contact to infectious tuberculosis does not provide any information about when and where the infection took place - it may have occurred years ago.