Mantoux Test (Purified Protein Derivative) is significantly positive when the erythema measures?

AIIMS Delhi NO- 2019

Medical & Surgical Nursing

Hard

Appeared in: AIIMS Delhi NO- 2019

Explanation

The Mantoux test is read by measuring the diameter of the induration (palpable, raised, hardened area), not the erythema (redness).
An induration of 15 mm or greater is considered a positive result for all individuals, including those with no known risk factors for tuberculosis (TB).
Because the question does not specify any patient risk factors, the 15 mm threshold is the only option that is universally interpreted as a significant positive result.

Option B: This range is generally considered negative. Only the upper end of this range (5 mm to 9.9 mm) would be considered positive, and only for individuals in the highest-risk category (e.g., HIV-positive, recent close contacts of an active TB case).
Option C: This range is only considered positive for individuals in the highest-risk groups, such as those who are HIV-positive, recent contacts of an infectious TB case, or have evidence of old, healed TB on a chest X-ray.
Option D: This range is considered positive only for individuals in medium-risk groups. This includes healthcare workers, recent immigrants from high-prevalence countries, and residents of congregate settings like prisons or nursing homes.

Clinical Relevance

Nursing practice connection: This is primarily an exam-oriented knowledge point with limited direct bedside application, so retain Interpretation of the Mantoux Tuberculin Skin Test (TST) as background academic context rather than a clinical decision trigger.
Correctly interpreting a Mantoux test is a critical nursing skill to ensure proper screening for TB, a major public health concern in India. Misinterpretation can lead to either unnecessary, costly follow-up or missed cases of latent or active TB.
Nurses are responsible for administering the PPD, reading the result at 48-72 hours, and accurately documenting the induration in millimeters (not just 'positive' or 'negative').
A key patient safety issue is distinguishing induration from erythema. A large red area with no hardening is a negative result. Documenting this incorrectly could lead to inappropriate treatment.

How to Approach the Question

First, identify the core concept: interpretation of a Mantoux test.
Recognize the discrepancy in the question: it asks about 'erythema' (redness), but the correct parameter to measure is 'induration' (hardness). This is a common point of confusion and a likely testing point.
Analyze the term 'significantly positive'. Understand that the significance of a result depends on the patient's risk factors, which are not provided in the question.
Evaluate the options based on standard interpretation guidelines. Since no risk factors are given, the most reliable answer is the one that is considered positive for everyone.
Select the option representing the threshold for a positive result in a low-risk individual (15 mm or greater), as this is a universally positive finding.

Concept Tested & Keywords

Concept Tested: Interpretation of the Mantoux Tuberculin Skin Test (TST)
Stem keywords: Mantoux Test, Purified Protein Derivative, PPD, positive, erythema
Lead-in keywords: significantly positive
Negative lead-in flag: false

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

E6 Medicine Harrison 22e Part 1 p. 1442-1444