In TB screening, which induration size is positive for immigrants, healthcare workers, and incarcerated persons?

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Tuberculin skin testing interprets the size of induration after 48–72 hours, with the positive cutoff guided by how likely someone is to have or acquire TB. For groups with higher risk—such as immigrants from TB-endemic regions, healthcare workers with exposure, and incarcerated individuals—a 10 mm or larger induration is considered positive. This threshold helps identify latent infection that could progress or spread in settings where exposure risk is greater, without labeling low-risk people as infected. In contrast, a 5 mm induration is reserved for the highest-risk situations (for example, recent contact with active TB, HIV infection, organ transplant, or severe immunosuppression), while a 15 mm cutoff is used for individuals with no known risk factors. Thus, a 10 mm induration is the appropriate positive threshold for the listed groups.