What does a positive Mantoux test indicate?

A positive Mantoux test indicates a reaction to the tuberculin purified protein derivative (PPD), which is used to determine if a person has been exposed to the bacteria that cause tuberculosis (TB). The test measures the immune response to a specific antigen found in the TB bacteria. When someone has been infected with TB, their immune system develops a response, resulting in a localized area of induration (swelling) at the site of injection.

This response does not necessarily mean that the person has active tuberculosis disease; it could also indicate a past infection or latent TB. Therefore, while a positive test is a strong indicator of TB infection, further evaluations, such as a chest X-ray or sputum test, may be necessary to determine if the infection is active or latent.

Understanding this mechanism is crucial for diagnosing and managing TB, especially in populations at risk of the disease. Other conditions, such as lung cancer, pneumonia, or influenza, do not produce the specific immune response measured by the Mantoux test, which is why they are not relevant to this question.