How should I interpret a positive tuberculin skin test (TST) result in a

A positive tuberculin skin test (TST) result in a patient with no symptoms of tuberculosis (TB) should be interpreted as an indication of latent TB infection rather than active disease. The threshold for a positive TST is an induration of 5 mm or larger, regardless of BCG vaccination history. Following a positive TST, the patient should be assessed for active TB through clinical evaluation and appropriate investigations. If active TB is excluded, consider further testing with an interferon-gamma release assay (IGRA) to confirm latent TB infection, especially if treatment decisions require additional evidence. If both TST and IGRA are positive and active TB is ruled out, offer treatment for latent TB infection to reduce the risk of progression to active disease. This approach applies to adults aged 18 to 65 who are close contacts of infectious TB cases, new entrants from high-incidence countries, healthcare workers, and immunocompromised individuals, with specific considerations for each group. Always ensure that active TB is excluded before initiating treatment for latent TB infection to prevent missing active disease that requires full treatment.