✨ Rationale for the MCQ ✨

A positive tuberculin test is indicated by induration of:
✅ (b) 10 mm or more in diameter

🩺 Understanding the Tuberculin Skin Test (TST)

The Mantoux test is used to detect tuberculosis (TB) infection. After injecting 0.1 mL of purified protein derivative (PPD) intradermally, the reaction is measured 48-72 hours later by assessing the size of the induration (raised, firm swelling), NOT the redness.

🔹 Interpretation of Induration Size:
📌 ≥5 mm – Considered positive in high-risk individuals (HIV, recent TB exposure, organ transplants, immunosuppressed).
📌 ≥10 mm – Considered positive in moderate-risk individuals (healthcare workers, recent immigrants, IV drug users, children <4 years).
📌 ≥15 mm – Considered positive in low-risk individuals with no known TB risk factors.

❌ Why Other Options Are Incorrect?

🚫 (a) 1-3 mm – Usually considered negative (no significant reaction).
🚫 (c) 7-9 mm – Borderline reaction; may be positive in high-risk individuals but not a general indicator.
🚫 (d) 4-6 mm – Usually considered negative unless in highly immunocompromised patients.

🔹 Example:
A 10 mm induration in a healthcare worker is positive, while the same reaction in a healthy adult with no risk factors is negative.