Sputum checking is so important that the patient should also master the correct method of sputum retention, otherwise it will directly affect the sputum test results. The correct method of sputum retention is to rinse the mouth with water several times before retaining sputum to remove food residues and some miscellaneous bacteria from the mouth. The retained sputum should be the sputum coughed up from the trachea after coughing hard, and then put it in the sputum box for examination. Do not spit saliva or nasal mucus into the sputum box as this may affect the sputum examination results. For those who need to check sputum for the first time, the doctor requires three sputum specimens: 1) immediate sputum: sputum coughed up at the time of consultation, 2) night sputum: sputum coughed up in the evening of the previous day, 3) early morning sputum: sputum coughed up deeply after waking up, of which the first sputum coughed up in the early morning has the best effect.