Recently, two patients who had coughing and blood in sputum for 2 or 3 months were admitted to the ward at the same time. Old He, who was over 40 years old, had his braces removed by tracheoscopic forceps (Anhui TV had reported on this), and the sputum and blood were caused by the braces inhaling into the trachea, so he was fine after removal; Old Pei, who had smoked for more than 30 years and was 56 years old, was not so lucky, and was clearly diagnosed as lung cancer through CT and tracheoscopy, and needed chemotherapy and other treatments. So, what is blood in sputum? And what is the cause of blood in sputum? Blood in sputum is a small amount of hemoptysis, blood-like sputum mixed with sputum, or bright red blood spots in sputum. Hemoptysis refers to bleeding from the inspiratory tract below the throat through the mouth. According to the amount of hemoptysis, it can be classified as blood in sputum and hemoptysis with large mouth. Hemoptysis refers to bleeding from the whistle below the larynx, which is expelled from the oral cavity by coughing. Hemoptysis must first be differentiated from oral, pharyngeal, and nasal bleeding. Hemoptysis must also be distinguished from hematemesis (upper gastrointestinal bleeding), which often has a history of peptic ulcer, cirrhosis, and other symptoms such as nausea and vomiting. There are many causes of hemoptysis, mainly the following four types of diseases: (1) diseases of pulmonary origin, such as tuberculosis, pneumonia, lung abscess, lung cyst, lung cancer, etc.; (2) bronchial diseases, such as bronchitis, bronchiectasis, bronchial tuberculosis, benign or malignant bronchial tumors, bronchial stones, bronchial foreign bodies, etc.; (3) cardiovascular and pulmonary vascular diseases, such as left heart failure, mitral stenosis, pulmonary arteriovenous fistula, pulmonary hypertension, pulmonary embolism, etc. (4) other systemic diseases, such as acute infectious diseases, leukemia, systemic lupus erythematosus, Wegener’s granulomatosis, etc. It is still clinically common to see lung and bronchial diseases, and a detailed medical history is helpful for diagnosis. In young adults, hemoptysis should pay more attention to tuberculosis, pneumonia, bronchiectasis and other diseases; the possibility of lung cancer and tuberculosis increases in middle-aged and older hemoptysis. Patients with hemoptysis should undergo appropriate tests, such as chest X-ray, chest CT, bronchoscopy, routine blood tests, coagulation function, autoimmune antibodies, and cardiac ultrasound, to help determine the cause of hemoptysis. In conclusion, hemoptysis is a very important clinical sign, and regardless of the amount of hemoptysis, it should be taken very seriously and should be seen by a doctor in a timely manner to avoid delay in treatment.