In tuberculin skin test (mountex test), a standard substance protein purified derivative (PPD) can be injecte… - NORCET 3 - 2022 (Shift-2)

NORCET 3 - 2022 (Shift-2)

Medical & Surgical Nursing

Easy

Appeared in: NORCET 3 - 2022 (Shift-2)

Explanation

The Mantoux test is a diagnostic tool for tuberculosis that relies on a delayed-type hypersensitivity reaction.
To elicit this reaction, the Purified Protein Derivative (PPD) antigen must be placed within the dermis, the layer of skin rich in immune cells.
An intradermal injection is the only route that correctly deposits the antigen into this layer, creating a localized bleb or wheal.
This localization is critical for the subsequent measurement of induration (hardening), which indicates a positive cellular immune response.

Option A: An intramuscular injection delivers the substance into the muscle tissue, which is too deep. The PPD would be absorbed systemically, failing to produce the required localized skin reaction for diagnosis.
Option C: An intravenous injection administers the substance directly into the bloodstream. This is incorrect and dangerous for a skin test, as it would bypass the skin entirely and could cause a systemic reaction.
Option D: A subcutaneous injection delivers the substance into the fatty tissue beneath the dermis. This is also too deep for a Mantoux test and would result in unreliable absorption and an inaccurate reading.

Visual 1: Diagram - A cross-section of the skin showing the different angles and needle depths for intradermal (10-15°), subcutaneous (45°), and intramuscular (90°) injections. This visually clarifies why the intradermal route is unique.
Visual 2: Image - A photograph of a positive Mantoux test on a forearm, clearly showing the raised, hardened induration that needs to be measured, distinct from any surrounding redness.

Clinical Relevance

Nursing practice connection: This is primarily an exam-oriented knowledge point with limited direct bedside application, so retain Administration route for Tuberculin Skin Test (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.
An incorrect technique, such as injecting too deeply, can lead to a false-negative result, potentially delaying diagnosis and treatment for an infected individual and posing a public health risk.
What if? If a wheal does not form upon injection, it indicates the PPD was likely injected subcutaneously. The procedure must be repeated immediately at another site (at least 2 inches away) to ensure an accurate test.

How to Approach the Question

First, identify the core of the question: it asks for the administration route of the 'tuberculin skin test', also known as the 'Mantoux test'.
Recall the different parenteral injection routes: Intramuscular (IM), Intradermal (ID), Intravenous (IV), and Subcutaneous (SC).
Associate the specific test with its required route. The Mantoux test is a classic example of a procedure requiring an intradermal injection.
Think about the purpose of the test. It's a 'skin test', meaning the reaction needs to happen in the skin to be visible and measurable. This points away from deeper routes like IM or SC and the systemic route of IV.
Select 'Intra-dermally' as it is the standard, required route for depositing the PPD into the correct skin layer to produce a diagnostic wheal and subsequent induration.

Concept Tested & Keywords

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