Mantoux test is done in tuberculosis by injecting 1 TU of PPD in 0.1 ml on the flexure surface of the forearm and reading is taken after:

Appeared in: Haryana CHO -2023

Explanation

The Mantoux test assesses a delayed-type (Type IV) hypersensitivity reaction, which takes time to fully manifest.
The immune response begins hours after the injection but reaches its maximal induration (hardness) between 48 and 72 hours.
While the reading can be performed anytime within this window, 72 hours is considered the ideal time.
Reading at 72 hours ensures that the peak reaction is captured, which reduces the likelihood of a false-negative result if an individual's immune response is slower to develop.

Option A: This is too early. The delayed-type hypersensitivity reaction has not had sufficient time to develop. A reading at 12 hours would almost certainly be negative, even in an infected person.
Option B: This is still too soon. While a reaction may start to become visible, it will not have reached its peak size. Reading at 24 hours can lead to underestimation of the induration and a false-negative result.
Option C: This is the earliest point in the acceptable reading window (48-72 hours). While a reading at 48 hours is valid, it is not considered the ideal time because the reaction may not have fully peaked in all individuals.

Clinical Relevance

Nursing practice connection: This is primarily an exam-oriented knowledge point with limited direct bedside application, so retain Procedure and timing for reading the Mantoux tuberculin skin test as background academic context rather than a clinical decision trigger.
Accurate timing and measurement of the Mantoux test are critical for diagnosing latent TB infection, which allows for preventive therapy to stop progression to active disease.
A false-negative reading (e.g., reading too early) can lead to a missed diagnosis, leaving the patient at risk and potentially allowing for community transmission if they develop active TB.
Patient education is a key nursing responsibility. The nurse must clearly instruct the patient on when to return for the reading, as a missed appointment invalidates the test.

How to Approach the Question

First, identify the core question, which is about the specific timing for reading a Mantoux test.
Recall that the Mantoux test is a 'delayed' hypersensitivity test. This physiological principle immediately helps eliminate very short timeframes like 12 or 24 hours, as the immune reaction needs more time to develop.
Remember the standard clinical guideline for the reading window, which is 48 to 72 hours.
Analyze the options provided. Both 48 hours and 72 hours fall within the correct window.
In such cases, apply clinical reasoning: to ensure the most accurate result and avoid false negatives, the reading should be done when the reaction is at its maximum. The reaction peaks towards the end of the window.
Therefore, select 72 hours as the most precise and ideal answer.

Concept Tested & Keywords

Concept Tested: Procedure and timing for reading the Mantoux tuberculin skin test.
Stem keywords: Mantoux test, tuberculosis, PPD, reading
Lead-in keywords: taken after
Negative lead-in flag: false

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Practise the full Haryana CHO -2023

Attempt every question from this paper in a timed mock, then review the full solution for each one.