The TB skin test, or PPD test, is weakly positive for Mycobacterium tuberculosis infection or BCG vaccination in the past. For normal people, a weakly positive PPD test does not require BCG vaccination. If the PPD test is done to determine whether there is tuberculosis, a weak positive is not diagnostic, and further refinement of other tests is needed, usually requiring multiple sputum checks, that is, sputum looking for antacid bacilli. If the sputum is positive, the diagnosis is tuberculosis. If the sputum is negative, a comprehensive judgment needs to be made based on the patient’s clinical symptoms, lung imaging and related blood tests and other items. At present, a large proportion of patients with pulmonary tuberculosis are sputum-negative, and treatment is also needed for such patients.