In the tuberculin test, the area of induration is measured after?

NVS Staff Nurse - 2019

Community Health Nursing

Easy

Appeared in: NVS Staff Nurse - 2019

Explanation

The tuberculin test result should be read between 48 and 72 hours after administration.
This timing is crucial because the test relies on a Type IV delayed-type hypersensitivity reaction, which peaks during this window.
Reading the test before 48 hours may lead to a false-negative result as the reaction may not have fully developed.
Reading after 72 hours is also discouraged as the induration may begin to wane, potentially causing an underestimation of the reaction size.

Option B: This option is too restrictive. While a reading at 72 hours is acceptable, the valid period for reading the test is a window from 48 to 72 hours.
Option C: This option includes the 24-hour mark, which is too early to read the test. The delayed hypersensitivity reaction has not reached its peak at 24 hours, which can lead to a false-negative result.
Option D: This option is incorrect because it starts too early (at 24 hours) and ends too soon (at 48 hours), potentially missing the peak reaction which can occur up to 72 hours.

Clinical Relevance

Nursing practice connection: This is primarily an exam-oriented knowledge point with limited direct bedside application, so retain Timing for reading a Tuberculin (Mantoux) test as background academic context rather than a clinical decision trigger.
Accurate timing for reading the Mantoux test is critical for the correct diagnosis and management of tuberculosis (TB) infection. A misread test can lead to either unnecessary treatment or failure to treat a latent infection.
Nurses are responsible for administering the PPD, educating the patient on the importance of returning for the reading within the 48-72 hour window, and instructing them not to scratch or tightly cover the site.
What if? If a patient returns at 96 hours with a visible reaction, the test is considered invalid. The result cannot be reliably interpreted, and the test must be repeated (usually on the other arm).

How to Approach the Question

Identify the core question: it asks for the specific time frame for measuring a tuberculin test reaction.
Recall the type of immune reaction involved. The tuberculin test is a classic example of a delayed-type (Type IV) hypersensitivity.
Understand that 'delayed' means the reaction takes time to develop, typically peaking after 2-3 days.
Evaluate the options based on this knowledge. Any time frame including 24 hours is too early. The peak occurs between 48 and 72 hours.
Select the option that represents this peak window most accurately and completely.

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