One of the diagnostic tests for Tuberculosis?

KPSC Staff Nurse - 2017

Medical & Surgical Nursing

Easy

Appeared in: KPSC Staff Nurse - 2017

Explanation

The Mantoux test, also known as the Tuberculin Skin Test (TST), is a standard screening tool used to identify individuals who have been infected with Mycobacterium tuberculosis.
The test works by detecting a delayed-type (Type IV) hypersensitivity reaction from the body's T-cells to a purified protein derivative (PPD) of the tuberculin antigen.
A small amount of PPD is injected intradermally into the forearm, and the site is examined 48 to 72 hours later.
A positive result is determined by measuring the diameter of the induration (a palpable, raised, hardened area), not the redness (erythema).

Option B: A blood culture is used to detect systemic infections where bacteria are present in the bloodstream (bacteremia/septicemia). While TB can disseminate (miliary TB), blood culture is not the primary or routine method for diagnosing pulmonary TB.
Option C: A complete blood count (CBC) is a non-specific test. It provides general information about blood cells but cannot identify the specific pathogen causing an infection. Findings in TB are not diagnostic.
Option D: The Widal test is a serological test specifically designed to detect antibodies against the Salmonella bacteria that cause typhoid fever.

Clinical Relevance

Nursing practice connection: This is primarily an exam-oriented knowledge point with limited direct bedside application, so retain Diagnostic methods for Tuberculosis (TB) infection as background academic context rather than a clinical decision trigger.
Nurses are responsible for the correct administration of the PPD injection to form a proper wheal, accurately reading the induration size at 48-72 hours, and educating the patient to not scratch or cover the site.
It is critical to understand that a positive Mantoux test indicates TB infection but does not distinguish between latent TB infection (LTBI) and active TB disease. A positive result requires follow-up with a chest X-ray and possibly sputum analysis.
What if? If a patient has a history of receiving the BCG (Bacillus Calmette-Guérin) vaccine, they may have a false-positive Mantoux test. In such cases, an Interferon-Gamma Release Assay (IGRA) blood test is a more specific alternative as it is not affected by prior BCG vaccination.

How to Approach the Question

First, identify the key concept in the question, which is finding a 'diagnostic test for Tuberculosis'.
Next, systematically review each option to determine its primary use.
Recall or deduce that the Mantoux test is a classic screening method for TB exposure.
Eliminate the other options by identifying their correct indications: Blood culture for sepsis, Complete blood test as a general non-specific screen, and Widal test for typhoid fever.
Conclude that the only test listed that is used for Tuberculosis is the Mantoux test.

Concept Tested & Keywords

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