The Mantoux test is a diagnostic tool used to determine if a person has been exposed to the bacterium that causes tuberculosis (TB). It involves injecting a small amount of purified protein derivative (PPD) into the skin of the forearm. After 48 to 72 hours, a healthcare professional examines the injection site for any swelling or redness, which indicates a possible TB infection. A positive result does not confirm active tuberculosis but suggests that the person has been exposed to the bacteria at some point. Further tests, such as a chest X-ray or sputum test, may be needed to confirm whether the infection is active or latent.