There are various methods of sputum examination, and in order to ensure the positive rate of sputum examination, qualified sputum specimens need to be retained. The correct method of sputum retention is to rinse the mouth with water several times before sputum retention to remove contaminants such as food residues in the mouth, then cough hard and cough out the deep sputum, place it in the previously prepared sputum examination box and send it for examination in time. Generally the sputum coughed up for the first time in the early morning has the best effect, but the specific duration of sputum retention depends on the requirements of the disease itself, for example, in patients suspected of tuberculosis and looking for tuberculosis bacteria in the sputum, it is recommended to retain sputum several times at different time periods to increase the positive rate, and even sputum can be retained for 24 hours to be sent for examination. Patients should strictly follow the instructions of their health care provider and keep qualified sputum specimens to facilitate early diagnosis of the disease.