PPD test is also called tuberculin test and the result is observed after 48-72 h. PPD test is the injection of tuberculin toxin into the skin and the result is observed after 48-72 h. Pay attention to the changes in the skin. If the skin only appears red and moist, or if the nodules that appear are small, <0.5cm, they are considered not to have been infected with Mycobacterium tuberculosis and are a negative result. If the diameter is >0.5 cm, it is a positive result, indicating infection with Mycobacterium tuberculosis. If the nodule is >2cm in diameter, it is a strong positive result, indicating possible active tuberculosis. Active tuberculosis also depends on sputum examination as well as imaging. If active tuberculosis is determined, a reasonable and regular anti-tuberculosis treatment is required.