This patient uses injection drugs, so she is at higher risk for exposure to or infection with Mycobacterium tuberculosis and should be screened for the pathogen, preferably with an interferon-γ release assay (IGRA). An IGRA or a tuberculin skin test (TST) can be used to diagnose tuberculosis, although neither differentiates between active disease and latent tuberculosis infection (LTBI). An IGRA can be used instead of a TST in all cases in which TST is recommended; however, an IGRA is preferred for persons from groups who are at high risk for not returning for interpretation of their TST result (such as injection drug users or homeless persons) and those who have received bacillus Calmette-Guérin as a vaccine or for cancer treatment. Although IGRA tends to be more expensive than TST, the resultant increase in rates of test completion are likely more cost-effective in persons at high risk for noncompletion of TST testing and also allows for improved public health efforts in the management of infected persons at significant risk for infection.

If the IGRA result is positive, then an evaluation for active disease includes review of symptoms (fever, night sweats, weight loss, cough, fatigue, chest pain), chest radiography, and possibly microbiologic assessment of sputum (or other involved fluid). LTBI can be diagnosed when active disease is ruled out. However, chest radiography or induced sputum examination is not used for screening for LTBI.