What causes someone to spit up blood?

The medical term for coughing up blood is hemoptysis. People with bronchitis and a heavy cough can sometimes cough up a bit of blood streaked sputum (mucus) for a few days. But coughing up a large amount of blood or having the symptom persist or recur are reasons to seek prompt medical evaluation. There are many possible reasons for hemoptysis. The first diagnostic test is usually a chest x-ray or chest CT scan. Whether the person is a smoker and what other symptoms such as fever, chest pain or weight loss help determine the diagnostic process.