Tuberculin test denotes?

NHM UP Staff Nurse - 2016

Applied Microbiology & Infection control

Easy

Appeared in: NHM UP Staff Nurse - 2016

Explanation

The Tuberculin test, or Mantoux test, detects a delayed-type (Type IV) hypersensitivity reaction to purified protein derivative (PPD) from Mycobacterium tuberculosis.
A positive reaction (induration) indicates that the individual's immune system has been previously sensitized to tubercle proteins.
This sensitization can result from a past or present TB infection (active or latent) or from prior BCG vaccination.
Therefore, the test denotes a state of sensitivity to these specific proteins, not active disease or protective immunity.

Option B: A positive tuberculin test does not indicate resistance. An individual can have a latent TB infection (which would yield a positive test) and still be at risk for reactivation and development of active TB disease.
Option C: The test does not measure susceptibility, which is the likelihood of acquiring a new infection in the future. It reflects a past or current immunological response to the bacteria.
Option D: Hypersensitivity to tuberculin proteins is not equivalent to protective immunity. A person can have a strongly positive test and still develop active tuberculosis. The test does not measure the effectiveness of the immune system in preventing the disease.

Clinical Relevance

Nursing practice connection: This is primarily an exam-oriented knowledge point with limited direct bedside application, so retain Interpretation of the Tuberculin (Mantoux) skin test as background academic context rather than a clinical decision trigger.
Accurate administration and reading are critical. The test must be read between 48 and 72 hours. A reading done too early or too late can be inaccurate.
The interpretation of a positive result is not universal; it depends on the patient's individual risk factors. A 5 mm induration can be positive for a high-risk individual (e.g., HIV positive), while a 15 mm induration is required for a low-risk individual to be considered positive.
A positive TST is often followed by a chest X-ray and sometimes sputum analysis to rule out active TB disease and determine if the patient has latent TB infection (LTBI), which may require treatment to prevent future activation.

How to Approach the Question

First, identify the core subject of the question, which is the 'Tuberculin test'.
Recall the fundamental purpose of this test. It is designed to see if the body's immune system has previously encountered the tuberculosis bacterium.
Understand that this encounter creates an immunological 'memory' or 'sensitivity', which results in a skin reaction when challenged with tuberculin proteins.
Evaluate each option against this core principle.
Option A correctly identifies this as 'sensitivity to tubercle proteins'.
Options B and D incorrectly equate this sensitivity with 'resistance' or 'protective immunity'. A reaction doesn't guarantee protection.

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