What is the minimum size of induration considered positive for a patient recently exposed to tuberculosis?

In the context of tuberculosis (TB) testing using the Mantoux tuberculin skin test, the size of induration is a critical factor in determining whether the test result is classified as positive. For individuals who have recently been exposed to TB, a minimum induration size of 5 mm is deemed positive. This threshold recognizes that recent exposure to the infection may produce a measurable immune response even in individuals who are otherwise healthy.

The 5 mm induration size is especially relevant for individuals with certain risk factors, including those who are HIV-positive, have had close contact with an infectious TB case, or have certain medical conditions that weaken the immune system. For these populations, a 5 mm induration indicates a significant response to the TB antigens, suggesting either infection or latent TB.

In contrast, different thresholds are used for other groups; for example, a 10 mm induration may be considered positive for individuals with moderate risk factors and is the standard cut-off for the general population without specific risk factors. The caution applied here is essential since the TB infection can put these individuals at higher risk for developing active disease.

Therefore, the correct answer regarding the minimum size of induration considered positive for a patient recently exposed to tuberculosis is 5 mm,