Coughing up blood or hemoptysis is a serious sign because it frequently indicates a serious underlying lung disease. Because many of the lung disease heralded by this sign are treatable, systematic and through evaluation is required in order to discover hemoptysis etiology.

The first step when evaluating hemoptysis is to establish if it is really hemoptysis (blood from the bronchial tree or lungs) or from other sites, mimicking hemoptysis. In most cases, the patient's clinical history suggests that the expectorated blood is indeed being coughed up from the lungs or respiratory tract but in some cases there may occur difficulties in distinguishing whether the blood source is  the respiratory system or two other sites: bleeding in the sinuses, upper respiratory tract or in the nasopharynx, or blood which originates the gastrointestinal tract and was regurgitated. A patient medical history of frequent nosebleeds and hoarseness or other voice changes suggests bleeding from the upper respiratory tract. The presence of gastrointestinal symptoms usually suggests hematemesis. Moreover, an emesis (vomit) with a coffee ground aspect may be determined if the blood from a respiratory source has been swallowed.

The most common cause of hemoptysis is tuberculosis. The hemoptysis resulting from this disease is usually mild to moderate and is commonly associated with other signs and symptoms such as unexplained weight loss, purulent sputum (thick, yellowish- white discharge) and a history of exposure to Mycobacterium tuberculosis.

Bronchitis, the inflammation and swelling of the bronchi represents another common cause of hemoptysis. In this case. the blood originates from recurrent coughing which irritates and eventually breaks the respiratory mucosal lining. The hemoptysis in bronchitis is usually mild and is usually associated with a purulent sputum , low-grade fever and wheezing.

Bronchiectasis, the chronic dilation with a consequent infection of the bronchioles and bronchi determined by the bronchial obstruction is another cause of hemoptysis. The patients with bronchiectasis often present with a mild to moderate hemoptysys, a severe cough accompanied by a  chronic purulent sputum. Lung cancer and bronchogenic carcinoma are important causes of hemoptysis. In these cases, the bleeding is the result of the necrosis of the tumor ), the rupture of  some small blood vessels in the tumor area, of the tumor invading activity of one of the pulmonary blood vessels (in which case massive bleeding occurs).

In pneumonia ( lung infection determined by a vaste variety of microorganism) other symptoms beside hemoptysis are: a high fever, cough, and chest pain.Other less common causes of hemoptysis are: pulmonary infarction or embolism, pulmonary AVM, trauma, heart diseases, vascular disorders, drug use, anticoagulant medication, pulmonary endometriosis, aspergilosis, and autoimmune disorders.