Tuberculosis screening is also known as a tuberculin test, often referred to as the PPD test. It is classified as positive, negative, or strongly positive. A positive result generally means that the person has been infected with Mycobacterium tuberculosis or has received BCG vaccination, while a strong positive result generally means that there is a possibility of active tuberculosis. A negative test generally means that the patient has not been infected with Mycobacterium tuberculosis and has not been vaccinated with BCG. Some people with poor immune status are also negative, such as those with malignant tumors, HIV infection, or in the acute phase of measles, etc. It is also possible for such patients to have a negative PPD test. Tuberculin test is not the basis for confirming the diagnosis. For patients with suspected tuberculosis infection, further imaging examinations and sputum searching for antacid bacilli and other related tests are needed to clarify the diagnosis.