What diameter of a raised lesion at a PPD injection site is considered positive for the test?

A raised lesion at a PPD (Purified Protein Derivative) injection site is considered positive based on the diameter of induration, which is the hardened area surrounding the injection site. The threshold for a positive test result varies depending on the individual's risk factors and health status.

In general, a diameter of 10 mm is commonly used as the cutoff for those with average risk for tuberculosis. However, in certain high-risk populations, such as individuals with HIV, recent contacts of active TB patients, or those with other immune-deficient states, a smaller induration of 5 mm may be considered positive.

Among the choices provided, a diameter of 12 mm is considered a significant positive reaction. This suggests a robust immunological response, indicating either previous exposure to tuberculosis or an active infection in those who might not otherwise meet the high-risk criteria. In a standard clinical context, especially for those with no additional risk factors, a raised lesion of this size indicates a strong likelihood of latent TB infection and would necessitate further investigation.

Thus, recognizing that a 12 mm diameter is a significant indication of a positive test helps ensure timely identification and potential treatment of tuberculosis in patients who might otherwise go undiagnosed.