A positive reaction to the Mantoux test indicates that?

HPSSC - 2015

Medical & Surgical Nursing

Easy

Appeared in: HPSSC - 2015

Explanation

A positive Mantoux test indicates that the individual has been exposed to Mycobacterium tuberculosis and has developed a cell-mediated immune response.
This reaction is a Type IV delayed-type hypersensitivity response to the purified protein derivative (PPD) injected into the skin.
It signifies sensitization to the bacteria but crucially does not differentiate between a latent infection (LTBI) and active TB disease.
Therefore, it is only evidence of past or present infection, not necessarily active illness.

Option A: A positive test alone does not confirm active TB. Many people have a latent TB infection (LTBI) where the bacteria are present but not causing illness. Active disease requires further confirmation.
Option B: This is a speculative statement. While there is a risk, most individuals (about 90-95%) with a latent TB infection will never develop active disease. The risk is higher for immunocompromised individuals but is not a certainty.
Option C: The test indicates sensitization, not protective immunity. The presence of a reaction means the immune system recognizes the bacteria, but it does not mean the person is protected from developing active disease in the future. In fact, it confirms they are carrying the bacteria (in the case of LTBI) and are at risk for reactivation.

Clinical Relevance

Nursing practice connection: This is primarily an exam-oriented knowledge point with limited direct bedside application, so retain Interpretation of a positive Mantoux test (Tuberculin Skin Test - TST) as background academic context rather than a clinical decision trigger.
Nurses are responsible for correctly administering the TST via intradermal injection, reading the result at 48-72 hours, and accurately measuring and documenting the induration in millimeters.
Patient education is a critical nursing role. Nurses must explain that a positive result means exposure, not necessarily active illness, and that follow-up tests like a chest X-ray are required to determine the next steps.
What if? If a patient has a positive TST but is from a country where BCG vaccination is common (like India), the result is less reliable. The nurse should anticipate that an Interferon-Gamma Release Assay (IGRA) blood test will be ordered, as it is not affected by prior BCG vaccination and provides a more accurate indication of TB infection.

How to Approach the Question

First, identify the core of the question: What is the direct meaning of a 'positive reaction' to a 'Mantoux test'?
Recall the mechanism of the test. It is a test of the immune system's memory (cell-mediated immunity). A reaction means the immune system has encountered the TB antigen before.
Evaluate the options based on this mechanism. 'Exposure' is the most direct and accurate term for the immune system having encountered an antigen.
Critically analyze the other options. 'Active tuberculosis' is a specific diagnosis requiring more than just a skin test. 'Will develop' is a prediction, not a current state. 'Immunity' is incorrect because the test shows sensitization, which can lead to disease, not protection from it.
Select the option that represents the most fundamental and accurate interpretation of the test result, which is exposure.

Concept Tested & Keywords

Concept Tested: Interpretation of a positive Mantoux test (Tuberculin Skin Test - TST)
Stem keywords: positive reaction, Mantoux test
Lead-in keywords: indicates that
Negative lead-in flag: false

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