Coughing up blood is not necessarily lung cancer. Among respiratory diseases, the three most common causes of coughing up blood are, first, bronchiectasis; second, pneumonia and lung abscess; and third, lung cancer. So how can we determine the cause? The best, simplest, and fastest method is to go to the hospital for a lung CT scan as soon as coughing up blood occurs. If the lung CT shows bronchiectasis, then bronchiectasis should be considered; if it shows an infiltrative lesion, then pneumonia should be considered; if it shows a tumor, then lung cancer should be considered at that time. However, there is also a scenario where blood is coughed up, but the lung CT is completely normal. What should be done then? This situation might be due to pharyngitis. Sometimes, severe coughing from pharyngitis can cause bleeding of the mucous membranes in the throat. In this case, there’s no need for excessive worry, as it may be caused by factors involving the throat. Cough gently, and if there’s no blood when coughing lightly, it’s likely not serious. However, if there's still blood in the sputum even when coughing lightly, it is recommended to undergo a bronchoscopy to check for tuberculosis or cancer in the bronchi.