What is sputum?
Sputum or phlegm is the discharge that is expectorated from the respiratory system. It is a combination of mucus produced by the airways combined with saliva from the mouth. It also contains other components including microorganisms, whole cells (like the immune cells), debris and dust even if there is no respiratory disease present. In the event of a respiratory disease, it may contain the components above in higher quantities and sometimes blood as well.
Meaning of Different Types of Sputum
Clear sputum (colorless) that is slightly sticky and a bit viscous (thicker than water) is accepted as normal sputum. It is produced and secreted in moderate amounts to moisten the respiratory tract and trap dust and microorganisms (mucus) and lubricate the mouth and aid with chewing, swallowing and digestion (saliva). While any expectorated sputum is considered to be abnormal, small amounts of sputum can be coughed up or spat out with effort even in the absence of any respiratory pathology.
However, in certain conditions, particularly related to irritation of the respiratory tract, the amount of sputum may become excessive. In these pathological cases, the color, texture and even odor of the sputum may change. These variations may give an indication of the possible cause.
Normal, clear sputum is a serous discharge.
Large amounts of clear, frothy or pink sputum that is of a similar consistency as normal sputum may be a sign of pulmonary edema, which is an accumulation of fluid in the lungs. If it extremely profuse and lasting for weeks or months, then it may be due to lung cancer.
Frothy sputum is caused by surfactant in the lung alveoli which reduces the surface tension of the sputum. It indicates that the sputum had contact with the lung alveoli or originated from this site.
Mucoid, mucopurulent or purulent sputum is thicker and often more sticky than normal sputum. This is partly due to the greater mucus production coupled with pus in the purulent types.
Apart from the consistency, the color of purulent sputum may vary from white or gray to yellow, green, rust-colored or brown. It may also have a pink tinge (blood streaked) which may be due to a small quantity of blood.
Mucoid sputum is a sign of non-infectious airway disease like chronic bronchitis (COPD) and asthma or may occur in the early stages of infection. Mucopurulent sputum is an indication of infection of the respiratory tract, particularly of the bronchi or lungs – acute bronchitis and pneumonia.
Sputum may be blood stained where the normal sticky or mucopurulent thick consistency becomes thinner due to the presence of varying amounts of blood. In severe cases involving the coughing up of large amounts of blood (hemoptysis), the consistency of the sputum may be the same viscosity as blood and little or no sputum may be visible. Blood stained sputum may be due to tuberculosis, bronchiectasis, pulmonary embolism or lung cancer.