Mantoux test considered positive if redness is more than ...?

AIIMS Raipur NO - 2017 (Shift-1)

Medical & Surgical Nursing

Medium

Appeared in: AIIMS Raipur NO - 2017 (Shift-1)

Explanation

The question contains a common misconception; the Mantoux test is interpreted by measuring the palpable, raised, hardened area of induration, not the area of redness (erythema).
An induration of 10 mm or more is considered a positive result for individuals at moderate risk for tuberculosis (TB).
This moderate-risk category includes healthcare workers, recent immigrants from high-prevalence countries, residents of high-risk congregate settings (like nursing homes), and children under 4 years of age.
Therefore, among the given choices, 10 mm is the standard threshold for a positive test in this context.

Option B: An 8 mm induration is not a standard cutoff value. It would be considered positive only in high-risk individuals (where the threshold is 5 mm or more) but negative for moderate and low-risk groups.
Option C: A 12 mm induration is not a standard cutoff value. A reaction of this size would be considered positive because it is greater than the 10 mm threshold for moderate-risk individuals.
Option D: A 14 mm induration is not a standard cutoff value. It would be considered positive for high and moderate-risk groups but would be considered negative for low-risk individuals, for whom the cutoff is 15 mm or more.

Visual 1: Diagram - A clear illustration showing a forearm with a positive Mantoux test reaction, with a ruler correctly measuring the transverse diameter of the induration, explicitly labeling the induration versus the surrounding erythema.
Visual 2: Chart - A summary table outlining the three standard cutoffs for a positive Mantoux test (≥5 mm, ≥10 mm, ≥15 mm) and listing the specific patient populations that fall into each risk category.

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 as background academic context rather than a clinical decision trigger.
Correctly interpreting a Mantoux test is a critical nursing skill for screening for TB exposure. A misinterpretation can lead to either a missed diagnosis or unnecessary anxiety and treatment.
A positive Mantoux test indicates that the person's body was previously infected with TB bacteria. It does not differentiate between latent TB infection and active TB disease. Further evaluation, such as a chest X-ray and sputum analysis, is required to diagnose active TB.
Nurses are responsible for educating patients to return for the reading within 48-72 hours and not to scratch the site, as this can affect the result.

How to Approach the Question

First, identify the core subject of the question, which is the interpretation of a Mantoux test.
Recognize the keyword 'redness'. This is a critical distractor. Recall from your training that the test measures 'induration' (hardening), not 'redness' (erythema). This is a common point of confusion tested in exams.
Recall the standard thresholds for a positive Mantoux test based on induration size: 5 mm, 10 mm, and 15 mm, each corresponding to different risk levels.
Evaluate the given options (10, 8, 12, 14 mm). Of these, only 10 mm is a standard, widely used cutoff.
Select 10 mm as the best answer, as it represents the threshold for moderate-risk individuals, a common standard in clinical practice and for healthcare workers themselves.

Concept Tested & Keywords

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