Final answer:
A positive PPD test indicates TB exposure and a cellular immune response, but it does not definitively mean the person has active TB, is infectious, or has TB antibodies. False positives can occur for individuals vaccinated with BCG, necessitating additional tests to confirm TB infection.
Step-by-step explanation:
A positive PPD (Purified Protein Derivative) test indicates that an individual has been exposed to Mycobacterium tuberculosis and has developed a cellular immune response to it. This is considered a delayed hypersensitivity reaction. The presence of a raised, red, hard area known as induration at the test site signifies a positive result due to accumulation of activated macrophages. However, a positive PPD test does not necessarily mean that the person has active TB, is infectious, or has developed antibodies against TB - it only indicates exposure to the bacteria.
Individuals vaccinated with BCG may also have a positive PPD test result, leading to false-positive interpretations for active TB infection. Additional tests, such as chest radiographs, may be required to confirm TB exposure, especially in the presence of clinical symptoms consistent with tuberculosis.