Induration of 5 mm or greater on a TB skin test is considered positive in which population?

• A. HIV
• B. Recent immigrants
• C. Homeless
• D. IV drug users

Answer: (A)

TB skin test interpretation uses different induration cutoffs based on infection risk and immune status. When the immune system is weakened, as in HIV infection, the body's reaction to TB antigens can be blunted, so a smaller induration can still indicate infection. That’s why an induration of 5 mm or greater is considered a positive result in people with HIV.

For others who aren’t immunocompromised, the threshold for positivity is higher (often 10 mm or 15 mm, depending on specific risk factors). So while recent immigrants, the homeless, or IV drug users may be at increased risk, a 5 mm induration alone would not automatically be labeled positive in those groups unless additional risk factors or immunosuppression are present.