What is the minimum size of a positive TB skin test for patients who are HIV positive?

In the context of tuberculosis (TB) screening, the interpretation of the tuberculin skin test (TST) results varies based on the individual's risk factors and underlying health conditions. For individuals who are HIV positive, a TST induration of 5 mm or greater is considered a positive result.

This lower threshold recognizes the immunocompromised state of HIV patients, which makes them more susceptible to TB infection. Therefore, even a small induration indicates significant exposure and warrants further evaluation and possible treatment, as these patients have a higher risk of severe TB disease.

In contrast, the thresholds for those who are not immunocompromised, such as healthy individuals, generally require a greater induration (10 mm) to be deemed positive. For healthcare workers or individuals with close contact to someone with active TB, a 15 mm induration might be used.

Hence, for a patient living with HIV, a reaction of 5 mm or more is the standard cutoff for a positive TB skin test, highlighting the importance of early detection and intervention in this vulnerable population.