What does induration indicate in TB testing?

• A. That the person has been exposed to TB, developed antibodies, and is infected with TB bacteria, but this doesn't tell if the infection is active or latent so further testing is required.
• B. Immediate active TB
• C. Immunization against TB
• D. That the person has latent TB only

Answer: (A)

Induration from a TB skin test reflects a delayed-type hypersensitivity reaction that occurs when the immune system has been sensitized by exposure to TB antigens. This means the person has been infected with TB bacteria (or exposed to them) at some point and developed an immune response. However, this reaction alone does not indicate whether the infection is active or latent; to determine disease status, further tests such as a chest X-ray and sputum analysis are needed. The reaction isn’t a direct measure of immunization status, and a positive result doesn’t prove active disease or latent infection by itself.