In tuberculin skin test (mountex test), a standard substance protein purified derivative (PPD) can be injected on fore arm via?

Appeared in: NORCET -3 (Shift-2)

Explanation

The Mantoux test is a delayed hypersensitivity skin test that requires a localized reaction.
The intradermal route deposits the PPD antigen into the dermis, the layer of skin rich in immune cells.
This placement allows for the formation of a visible and palpable wheal, followed by a measurable induration if the person has been exposed to TB.
The slow absorption from the dermis is essential for the delayed-type hypersensitivity reaction to develop and be assessed accurately.

Option A: Intramuscular injection places the substance deep into the muscle tissue, leading to rapid systemic absorption. This prevents the localized skin reaction (induration) needed for a diagnostic reading.
Option C: Intravenous injection administers the substance directly into the bloodstream. This is incorrect and potentially harmful for a skin test antigen, as it would cause a systemic reaction rather than a localized diagnostic one.
Option D: Subcutaneous injection places the substance into the fatty tissue beneath the skin. This would lead to variable absorption and would not produce the distinct, measurable induration required for an accurate Mantoux test reading, often resulting in a false-negative.

Clinical Relevance

Nursing practice connection: This is primarily an exam-oriented knowledge point with limited direct bedside application, so retain Administration route for the Tuberculin (Mantoux) test as background academic context rather than a clinical decision trigger.
Correct administration of the Mantoux test is a fundamental nursing skill critical for accurate tuberculosis screening.
A faulty technique, such as injecting too deeply (subcutaneously), can lead to a false-negative result, causing a delay in diagnosis and treatment for an infected individual.
Nurses must educate patients not to scratch or rub the area and to return for the reading within the 48-72 hour window.

How to Approach the Question

First, identify the core subject of the question: the 'tuberculin skin test' or 'Mantoux test'.
Recall that this is a diagnostic test for tuberculosis exposure, not a vaccination or treatment.
Think about the purpose of the test: to create a localized, visible, and palpable immune reaction on the skin.
Consider the different parenteral routes. The intradermal route is specifically designed to place substances just under the top layer of skin to observe for a local reaction.
Eliminate other routes: Intramuscular and intravenous routes are for systemic absorption, and subcutaneous is for slower systemic absorption, none of which are suitable for a localized skin test.

Concept Tested & Keywords

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E6 Parks TextBook of Preventive & Social Medicine part 1 — Subpart B (pp 202-403 of 604) p. 25-27

E6 Ghai Essential Pediatrics(pp 26-904 of 913) p. 257-259

E6 Anatomy Applied Ashalatha 4e p. 232-234

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