A PPD test should be read within how many hours after injection?

• A. 24-48 hours
• B. 48-72 hours
• C. 72-96 hours
• D. 12-24 hours

Answer: (B)

The reading window for a PPD (Mantoux) test targets the peak of a delayed-type hypersensitivity reaction to tuberculin. This response takes about two to three days to develop, so evaluating the skin 48 to 72 hours after injection captures the most accurate induration size. Reading earlier often shows mainly redness with little true induration, while waiting longer than 72 hours can blur margins and reduce accuracy. So, the best timing is about 48–72 hours after administration.