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routine sputum culture

Alternative Names 
routine sputum culture,

This test attempts to detect and identify organisms in the sputum. Sputum is a secretion coughed up from the lungs. It is different than saliva, which comes from the mouth.

Who is a candidate for the test? 
This test is ordered when the doctor suspects an infection in the lungs or bronchi, such as pneumonia or tuberculosis. The bronchi are the tubes that carry air to the lungs. In many cases, sputum will contain the infection-causing organism when a lung infection is present.

How is the test performed? 
The person is asked to cough deeply to bring up sputum. The sputum can then be spat into a cup. The sputum is taken to a laboratory, where it is placed in special containers. These containers have food and other things to help organisms, such as bacteria, grow. Any bacteria that grow in the containers can be identified.

What is involved in preparation for the test? 
No preparation is usually needed for this test. Specific instructions will be given if needed.

What do the test results mean? 
The results of this test usually take at least 48 hours. In some cases, up to six weeks may be needed to detect certain organisms. If a person gives a good sputum sample, it should not contain any organisms. Sometimes, a bad sample is taken, such as when a person simply spits into the cup. This sample may grow bacteria or other organisms, but does not give any useful information. This is because bacteria normally live in the throat and mouth. These bacteria do not usually cause an infection in the lungs.

If organisms are present in a good sputum sample, an infection is often present. The infection may be in the bronchi or deep in the lungs. Knowing the exact cause of an infection helps the doctor advise a specific therapy. For example, if specific bacteria are found, the doctor may want to give the person a specific antibiotic. In some cases, a person is given an antibiotic right away, before the test results are available. The doctor may then switch the antibiotic if a specific organism is found.

Author: David T. Moran, MD
Reviewer: eknowhow Medical Review Panel
Editor: Dr John Hearne
Last Updated: 27/02/2005
Potential conflict of interest information for reviewers available on request

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