Dark red blood clots in sputum are called blood in sputum. Most of them come from small amounts of blood seepage or bleeding from the lungs, such as pathologic bleeding from the bronchial tubes, and require prompt medical attention. Blood in sputum can also come from the lungs and bronchial tubes, including bronchiectasis, bronchopulmonary cancer, chronic bronchitis, bronchial mucosal ulcers and other bronchial diseases, pneumonia, lung abscess, tuberculosis and other lung diseases. In addition, cardiovascular diseases such as mitral valve stenosis and blood diseases such as leukemia and hemophilia may also present with blood in sputum. At the same time, some of the blood clots in sputum may also come from chronic inflammation of the nasal cavity caused by sinusitis, dry rhinitis and other mucous membrane edema after oozing blood. The causes of blood in sputum are many, long-term blood in sputum is recommended to go to the hospital in a timely manner, so as to avoid delaying the condition.