Sputum examination, i.e. sputum testing, can be used for the pathogenetic diagnosis of lung infectious diseases, the diagnosis of open tuberculosis, the diagnosis of lung cancer and the diagnosis of lung parasites. 1. Pathogenetic diagnosis of lung infectious diseases: the character of sputum can generally help diagnosis, for example, sputum with bad odor can indicate anaerobic infection. Smear of sputum can roughly identify the type of infecting bacteria. In addition, bacterial culture of sputum can identify the strain of bacteria and screen for sensitive drugs. 2. Diagnosis of open tuberculosis: finding Mycobacterium tuberculosis in sputum smear or culture of Mycobacterium tuberculosis in sputum can help to diagnose active tuberculosis. 3. Diagnosis of lung cancer: positive sputum exfoliative cytology can confirm the diagnosis of lung cancer. 4. Diagnosis of lung parasites: Parasites, eggs or trophozoites found in sputum can confirm the diagnosis of parasitic disease of the lungs. If there is any discomfort, it is recommended to consult a doctor in time for diagnosis and treatment.