A tuberculin skin test is read 72 hours after intradermal injection of 1 TU of PPD RT-23 in an adult. Using the standard Indian convention, induration of how many millimetres or more is taken as positive?

• A 5 mm or more
• B 10 mm or more ✓
• C 15 mm or more
• D 20 mm or more

Explanation

As per Park's textbook and Indian programme practice, induration of 10 mm or more measured at 72 hours is read as a positive tuberculin test, irrespective of prior BCG scar in adults. The 5 mm cut-off belongs to the immunocompromised category in CDC practice and is not the Indian convention. Erythema is ignored; only induration counts.

Reference: Park's Textbook of Preventive and Social Medicine, 27th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

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