Tuberculosis is identified in the laboratory by using one of the test called Mantoux test. It is more reliable and helps in the identification of TB Active persons. This test includes the procedure by injecting a small amount of PPD (Purified Protein Derivative) tuberculin intracutaneously. A small bubble is formed at the place where the tuberculin is injected. After 48-72 hours the test site will be examined. People who are exposed to tuberculosis will have a swelling at the place of injection, whereas TB negative person lacks the swelling.