Sputum is a mucousy substance (consisting of cells and other matter) that is secreted into the airways of the respiratory tract. Sputum is not the same as saliva, a substance secreted in the mouth to help with digestion.
If a lung cancer is present near the airways, the sputum of the patient sometimes contains cancer cells. To test for lung cancer, physicians may order a test called sputum cytology. A patient coughs up sputum, the sample is collected and then examined in a lab for the presence of cancer cells.
Some conditions that result in increased production of sputum include: