A variety of diseases and infections of the respiratory system can cause an individual to cough up blood. Blood in the lungs and airway may be symptomatic of a relatively minor infection or underlie a more serious chronic disease. The amount of blood ranges from a bit contained in phlegm or sputum to, in cases of massive hemoptysis, more than two cups in 24 hours. The appearance of the blood also varies, from small streaks to bright red clots.
Coughing up blood is most often a symptom of bronchitis. This respiratory infection causes a severe, persistent cough due to irritation and swelling of the bronchi, the airways branching from the windpipe to the lungs. A virus, including the common cold virus, usually triggers this condition. Inflammation of the airway and frequent coughing fits may produce mucus streaked with blood. Bronchitis is not often considered a serious medical concern and, unless the condition turns chronic, treatment is confined to medication to prevent irritation and coughing.
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