What is Sputum?

What is Sputum and What Causes it to be Increased?

photo of sputum on a tissue
What is sputum?. Wikimedia Commons/User Zhangmoon618

Definition: Sputum

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.  The terms sputum and phlegm are used interchangeably.

The term mucus may sometimes be used, but sputum refers to that mucus specifically secreted in the respiratory tract, whereas mucus may also be produced in the gastrointestinal trace, urological tract, and genital tract.

Source of Sputum

Sputum or phlegm is coughed up from the lower airways in the respiratory tract - the bonchi and trachea - rather than glands in the mouth and throat.

Sputum/Phlegm Colors and Meanings

Sputum can be many colors and consistency, and these can help define certain conditions.  For example:

  • Clear sputum is normal
  • White/gray sputum can be normal
  • Dark yellow/green sputum - A type of white blood cells known as neutrophils have a green color to them.  These types of white blood cells are attracted to the scene of bacterial infections, and therefore bacterial infections of the lower respiratory tract, such as pneumonia, may result in producing green sputum
  • Brown sputum - Brown sputum due to the presence of tar, is sometimes found in people who smoke.
  • Pink sputum - Pink, especially frothy pink sputum may come from pulmonary edema - a condition in which fluid and small amounts of blood leak from capillaries into the alveoli of the lungs.
  • Bloody sputum - Bloody sputum, even just a tract of blood tinged sputum, should always be evaluated.  Coughing up blood can be serious, and is the first sign of lung cancer in 7% of people.  Even 1 to 2 teaspoons of coughed up blood is considered a medical emergency.

Sputum Contents

Sputum is made up from secretions from cells lining the respiratory tract, dead cells, foreign matter than is breathed into the lungs, and white blood cells and other immune cells.

 In infections, bacteria may also be present in sputum, and sometimes blood as well in the case of lung cancer, trauma to the respiratory tract, damage to the airways, and pulmonary edema.

Conditions With Increased Sputum

Some conditions that result in increased production of sputum include:

Sputum Tests

Sputum may be analyzed in the lab to determine its contents and more.  Tests include:

  • Sputum culture - A sputum culture is done by placing a sample of a sputum in a growing media and looking for the presence of growth.  This may be done to determine that particular type of bacteria causing a pneumonia.  Once the bacteria strain is determined, the lab can then do further tests to figure out which antibiotic is most effective against that bacteria.
  • Sputum for tuberculosis - A sputum sample may be obtain to look for tuberculosis.
  • Sputum cytology - In sputum cytology as sample of sputum is evaluated under the microscope.  This can be done to look for signs of tuberculosis, or signs of cancer cells.  At one time it was thought that sputum cytology could a screen for lung cancer, but it is not an effective screening tool.  If cancer cells are found, however, it can be diagnostic of lung cancer.  Further tests will then need to be done to find out the location of the cancer.

Decreasing Sputum

There are a number of ways in which to decrease sputum production, but the most important step is to diagnose and treat the underlying cause.  With air pollution and smoking, the underlying cause is the body's attempt to rid itself of foreign matter, and an overproduction of sputum is a normal response.  In that case removing the source is the best approach.  Medications that may help decrease sputum include aerosol treatments and expectorants.  Treatments such as postural drainage may be effective in some situations.

Also Known As: phlegm


U.S. National Library of Medicine. Routine sputum culture. Updated 12/03/13. https://medlineplus.gov/ency/article/003723.htm

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