A 2 year old child has a Mantoux test reading of 12 mm × 12 mm after 48 hours. In this case :
First, the core concept here is the interpretation of the Mantoux (tuberculin skin test) in children. The size of the induration determines if the test is positive. For children under 4 years old, a 5 mm induration is considered positive. Since the reading is 12 mm, which is way above 5, it's a positive result. So the correct answer would relate to a positive TB test.
Now, the options might be about whether it's positive, needs further testing, or if it's a false positive. The wrong options could include thresholds for adults (like 10 mm) or incorrect interpretations like considering it negative.
In the explanation, I need to mention that in high-risk groups like young children, the cutoff is lower. Also, the wrong options might confuse with different age groups or use incorrect measurements (like 10 mm for adults but not for children). The clinical pearl would emphasize that in children <4 years, 5 mm is the threshold for a positive TB skin test. I should structure the explanation with the core concept, why the correct answer is right (using the 5 mm threshold), why others are wrong (like using adult criteria), the clinical pearl, and then state the correct answer.
**Core Concept**
The Mantoux test (tuberculin skin test) assesses for prior exposure to *Mycobacterium tuberculosis* or BCG vaccination. In children under 4 years, a 5 mm induration is considered positive due to higher risk of severe TB. Larger indurations (e.g., 12 mm) confirm a positive result requiring further evaluation.
**Why the Correct Answer is Right**
A 2-year-old with a 12 mm × 12 mm induration after 48 hours exceeds the 5 mm threshold for positivity in high-risk pediatric populations. This indicates either TB infection or BCG cross-reactivity. Positive results in children mandate chest X-ray and sputum testing to rule out active TB.
**Why Each Wrong Option is Incorrect**
**Option A:** Incorrect. A 10 mm threshold applies to adults with risk factors (e.g., HIV), not young children.
**Option B:** Incorrect. A 15 mm induration is not a standard threshold; the test is interpreted categorically, not by absolute size.
**Option C:** Incorrect. A negative test would show <5 mm induration in this age group.
**Clinical Pearl / High-Yield Fact**
Never apply adult TB skin test thresholds to children <4 years. Remember: **5 mm is the magic number** for positivity in this age group. BCG vaccination can cause false positives, but this is less common in unvaccinated populations.
**Correct Answer: C. Positive Mantoux test indicating TB infection**