Basic and Clinical Sciences (BCSE) 2025 – 400 Free Practice Questions to Pass the Exam

A positive tuberculin skin test (TST) indicates that an individual has been exposed to Mycobacterium tuberculosis, the bacteria that cause tuberculosis (TB), and has mounted an immune response to it. For an HIV-negative individual with no history of BCG vaccination, a TST reading greater than 10 mm of induration is considered significant. This level of induration suggests a higher likelihood of active or latent tuberculosis infection, especially given that this individual does not have any known risk factors or prior vaccination that would lead to a false positive result.

In this context, a TST result greater than 10 mm typically warrants further evaluation, including clinical assessment and possibly additional testing such as a chest x-ray or interferon-gamma release assays, to determine if active TB disease is present. The threshold of greater than 10 mm reflects a robust immune response, indicating that the immune system has recognized the antigens associated with TB exposure.