PPD skin test is one of the main means to determine whether the organism is infected with Mycobacterium tuberculosis. If there is a positive PPD test, different situations should be distinguished and treated separately as follows: 1. If the PPD test is generally or moderately positive, if there is no abnormality or no tuberculosis lesion by chest imaging examination and no clinical evidence of tuberculosis in other parts of the body, it can be considered as a person infected with M. tuberculosis or an immune reaction after BCG vaccination, and no special treatment is needed for such cases; 2. or moderate positive PPD test, suspicious symptoms of TB, abnormal chest imaging or high suspicion of TB lesions, negative TB bacteriological examination can be used as an auxiliary basis for TB diagnosis. Such cases should be further examined by other TB programs to clarify the diagnosis; 3. Strongly positive reaction of PPD test, sputum examination and chest X-ray can be done, if there are no suspicious symptoms of TB and chest imaging is normal. Such cases can be treated with anti-tuberculosis chemoprophylaxis with informed consent, and those without prophylaxis can be placed under medical observation; 4. Children under 3 years of age who have not received BCG vaccination and have a positive tuberculin test or a strong positive reaction with a history of close family contact with tuberculosis, accompanied by fever, wasting and other uncomfortable symptoms, should be further examined to rule out the presence of active tuberculosis in the body. Such cases should be managed according to the treatment of patients with smear-negative tuberculosis, regardless of whether there is active tuberculosis in the body; 5. Positive PPD test reactions in newborns and infants 4-8 weeks after BCG vaccination indicate that BCG vaccination has been successful and artificial immunity of the body has been established, but the strength of the reaction of tuberculin skin test after BCG vaccination is significantly weaker than that of natural infection with tuberculosis bacteria, and such cases do not require special No special treatment is needed in such cases.