How is latent tuberculosis infection (LTBI) diagnosed?

Latent tuberculosis infection (LTBI) is primarily diagnosed when a person has a positive result from a tuberculosis skin test (TST) or an interferon-gamma release assay (IGRA) blood test, without evidence of active tuberculosis disease. A positive test indicates that the person has been infected with Mycobacterium tuberculosis, but it does not mean they are sick with TB disease.

In the diagnosis of LTBI, the absence of active TB symptoms and a negative chest X-ray are also important considerations, as these help confirm that the infection is latent rather than active. Thus, while the correct answer emphasizes that a positive test result can indicate LTBI if there are no signs of active disease, it is also essential to understand that further evaluations might be necessary to rule out active TB, which is not indicated in the other options.

The importance of this approach lies in effectively identifying individuals who may need treatment to prevent the progression to active TB disease, especially in populations at higher risk.