Tuberculosis Skin Test: Understanding the Results

What does a positive TB skin test indicate?

a. you have been exposed to TB
b. you are actively infected with TB
c. the TB disease is currently dormant but may later become active
d. you have never been exposed to TB

Answer:

A positive TB skin test indicates that the individual has been exposed to the TB bacteria and their immune system is responding to it.

Explanation:

A positive Tuberculosis (TB) skin test, also known as the Mantoux tuberculin skin test, often indicates exposure to the TB bacteria. This specific test involves injecting bacterial proteins from M. tuberculosis under the skin. After a few days, a positive reaction, evidenced by a raised, hard, red area, suggests that the individual has been exposed to the bacteria and that the immune system is responding.

However, this does not necessarily mean that the individual is actively infected with TB. The cellular immune response could be due to a current infection or from prior exposure which led to the creation of memory T cells. Moreover, chest radiographs or other additional tests may be required to differentiate between active TB disease and latent TB infection. Therefore the test only confirms exposure to TB but does not specify whether the infection is active or dormant.