A positive tuberculin skin test indicates that a patient not immunized against tuberculosis __________.


a. is free of tuberculosis
b. is shedding Mycobacterium
c. has been exposed to tuberculosis antigens
d. is susceptible to tuberculosis
e. is resistant to tuberculosis

Verified step by step guidance

1. Understand the purpose of a tuberculin skin test (TST), which is used to determine if someone has been exposed to Mycobacterium tuberculosis.
2. Recognize that a positive TST indicates an immune response to the antigens of Mycobacterium tuberculosis.
3. Consider that a positive result does not necessarily mean active disease or shedding of bacteria, but rather exposure to the antigens.
4. Eliminate options that do not align with the concept of exposure, such as being free of tuberculosis or being resistant.
5. Identify the correct interpretation of a positive TST in a non-immunized individual, which is exposure to tuberculosis antigens.

Key Concepts

Tuberculin Skin Test

The tuberculin skin test (TST), also known as the Mantoux test, is a diagnostic tool used to determine if a person has been exposed to the tuberculosis (TB) bacteria. It involves injecting a small amount of purified protein derivative (PPD) into the skin and observing the reaction after 48-72 hours. A positive result indicates that the immune system has recognized the TB antigens, suggesting prior exposure or infection.

Mycobacterium tuberculosis

Mycobacterium tuberculosis is the bacterium that causes tuberculosis, a contagious disease primarily affecting the lungs but can also impact other parts of the body. Understanding its transmission and pathogenicity is crucial for interpreting test results. A positive tuberculin test does not confirm active disease but indicates that the immune system has encountered the bacteria at some point.

Immune Response to Tuberculosis

The immune response to tuberculosis involves the activation of T-cells and the production of specific antibodies against the TB antigens. A positive tuberculin skin test reflects a cell-mediated immune response, indicating that the individual has been exposed to the TB bacteria, whether through infection or vaccination. This concept is essential for understanding why a positive test does not necessarily mean active disease.