Two days after administration of the PPD test, a female health-care worker developed an area of redness and induration 12 mm in size at the injection site. This result means that she has

Two days after administration of the PPD test, a female health-care worker developed an area of redness and induration 12 mm in size at the injection site. This result means that she has

• A. an active case of tuberculosis.
• B. been exposed to M tuberculosis.
• C. developed protective immunity against tuberculosis.
• D. a result in the normal range for her risk group.

Answer: (B)

Interpreting a tuberculin skin test result revolves around the body's delayed-type hypersensitivity to TB antigens. A 12 mm induration read 48–72 hours after PPD injection in a health-care worker indicates a positive reaction, meaning she has been exposed to Mycobacterium tuberculosis and has developed immune sensitization. This does not mean she has active tuberculosis; the test cannot distinguish latent infection from active disease. To evaluate for active TB, further workup such as symptoms assessment, chest imaging, and microbiologic testing would be needed. The result also does not reflect protective immunity. In this risk group, an induration of 12 mm is considered positive, not a normal range.

Interpreting a tuberculin skin test result revolves around the body's delayed-type hypersensitivity to TB antigens. A 12 mm induration read 48–72 hours after PPD injection in a health-care worker indicates a positive reaction, meaning she has been exposed to Mycobacterium tuberculosis and has developed immune sensitization. This does not mean she has active tuberculosis; the test cannot distinguish latent infection from active disease. To evaluate for active TB, further workup such as symptoms assessment, chest imaging, and microbiologic testing would be needed. The result also does not reflect protective immunity. In this risk group, an induration of 12 mm is considered positive, not a normal range.