Occasional blood in sputum may be due to diseases such as tuberculosis, bronchiectasis, lung cancer and pneumonia. 1. Tuberculosis: the main symptoms are cough, blood in sputum, low fever, night sweats, etc. It is caused by infection of Mycobacterium tuberculosis in the lungs, and the diagnosis can be confirmed by perfecting sputum smear, positive tuberculin test and chest imaging. 2. Bronchial dilatation: the main symptoms are long-term recurrent cough, coughing up pus sputum, blood in sputum, fever, etc. It is a chronic inflammation of the lungs leading to bronchial deformation, and the diagnosis can be confirmed by perfecting the routine blood test, sputum culture, and chest imaging examination. 3. Lung cancer: there is no obvious symptom in early stage, but cough, blood in sputum, chest tightness, shortness of breath, chest pain, unexplained weight loss will appear in late stage, which can be diagnosed by perfecting chest imaging examination, lung biopsy and tumor markers. 4. Pneumonia: the main symptoms are coughing, coughing up sputum, blood in sputum, chest tightness, fever, etc. It is due to lung infection with bacteria, fungi, virus, mycoplasma, etc. The diagnosis can be confirmed by completing the sputum culture, blood routine, chest imaging examination, etc. There are many other causes of occasional blood in sputum, so it is recommended to seek timely medical treatment and diagnosis and treatment as soon as possible so as not to miss the condition.