A 22-year-old nursing student is screened before joining duty. Her Mantoux test shows an induration of 12 mm at 72 hours. In the Indian programme context, this reading is interpreted as:

• A Negative, since positivity requires 15 mm or more
• B Positive, confirming active pulmonary tuberculosis
• C Equivocal, requiring repeat testing after 3 months
• D Positive, indicating infection with tubercle bacilli ✓

Explanation

In India, following standard convention, an induration of 10 mm or more at 48 to 72 hours is taken as positive, indicating infection with tubercle bacilli. The test measures hypersensitivity due to infection, whether recent or old, and does not distinguish latent infection from active disease, so option B is wrong. Because BCG given at birth can produce small reactions, some texts use higher cut-offs in BCG-vaccinated children, but 10 mm remains the conventional threshold.

Reference: Park's Textbook of Preventive and Social Medicine, 26th ed.

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Written and medically reviewed by the StethoPrep medical team.