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Sputum Culture

What is a sputum culture?

A sputum culture is a test that checks for bacteria or another type of organism that may be causing an infection in your lungs or the airways leading to the lungs. Sputum, also known as phlegm, is a thick type of mucus made in your lungs. If you have an infection or chronic illness affecting the lungs or airways, it can make you cough up sputum.

Sputum is not the same as spit or saliva. Sputum contains cells from the immune system that help fight the bacteria, fungi, or other foreign substances in your lungs or airways. The thickness of sputum helps trap the foreign material. This allows cilia (tiny hairs) in the airways to push it through the mouth and be coughed out.

Sputum can be one of several different colors. The colors can help identify the type of infection you may have or if a chronic illness has become worse:

  • Clear. This usually means no disease is present, but large amounts of clear sputum may be a sign of lung disease.
  • White or gray. This may also be normal, but increased amounts may mean lung disease.
  • Dark yellow or green. This often means a bacterial infection, such as pneumonia. Yellowish-green sputum is also common in people with cystic fibrosis. Cystic fibrosis is an inherited disease that causes mucus to build up in the lungs and other organs.
  • Brown. This often shows up in people who smoke. It is also a common sign of black lung disease. Black lung disease is a serious condition that can happen if you have long-term exposure to coal dust.
  • Pink. This may be a sign of pulmonary edema, a condition in which excess fluid builds up in the lungs. Pulmonary edema is common in people with congestive heart failure.
  • Red. This may be an early sign of lung cancer. It may also be a sign of a pulmonary embolism, a life-threatening condition in which a blood clot from a leg or other part of the body breaks loose and travels to the lungs. If you are coughing up red or bloody sputum, call 911 or seek immediate medical attention.

Other names: respiratory culture, bacterial sputum culture, routine sputum culture

What is it used for?

A sputum culture is most often used to:

  • Find and diagnose bacteria or fungi that may be causing an infection in the lungs or airways.
  • See if a chronic illness of the lungs has worsened.
  • See if treatment for an infection is working.

A sputum culture is often done with another test called a Gram stain. A Gram stain is a test that checks for bacteria at the site of a suspected infection or in body fluids such as blood or urine. It can help identify the specific type of infection you may have.

Why do I need a sputum culture?

You may need this test if you have symptoms of pneumonia or another serious infection of the lungs or airways. These include:

What happens during a sputum culture?

Your health care provider will need to get a sample of your sputum. During the test:

  • A health care provider will ask you to breathe deeply and then cough deeply into a special cup.
  • Your provider may tap you on the chest to help loosen sputum from your lungs.
  • If you have trouble coughing up enough sputum, your provider may ask you to breathe in a salty mist that can help you cough more deeply.
  • If you still can't cough up enough sputum, your provider may perform a procedure called a bronchoscopy. In this procedure, you'll first get a medicine to help you relax, and then a numbing medicine so you won't feel any pain.
  • Then a thin, lighted tube will be put through your mouth or nose and into the airways.
  • Your provider will collect a sample from your airway using a small brush or suction.

Will I need to do anything to prepare for the test?

You may need to rinse your mouth out with water before the sample is taken. If you will be getting a bronchoscopy, you may be asked to fast (not eat or drink) for one to two hours before the test.

Are there any risks to the test?

There is no risk to providing a sputum sample into a container. If you had a bronchoscopy, your throat may feel sore after the procedure.

What do the results mean?

If your results were normal, it means no harmful bacteria or fungi were found. If your results were not normal, it may mean you have some kind of bacterial or fungal infection. Your provider may need to do more tests to find the specific type of infection you have. The most common types of harmful bacteria found in a sputum culture include those that cause:

An abnormal sputum culture result may also mean a flare-up of a chronic condition, such as cystic fibrosis or chronic obstructive pulmonary disease (COPD). COPD is a lung disease that makes it hard to breathe.

If you have questions about your results, talk to your health care provider.

Learn more about laboratory tests, reference ranges, and understanding results.

Is there anything else I need to know about a sputum culture?

Sputum may be referred to as phlegm or mucus. All terms are correct, but sputum and phlegm only refer to the mucus made in the respiratory system (lungs and airways). Sputum (phlegm) is a type of mucus. Mucus can also be made elsewhere in the body, such as the urinary or genital tract.

References

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  13. UW Health [Internet]. Madison (WI): University of Wisconsin Hospitals and Clinics Authority; c2020. Health Information: Sputum Culture: Results; [updated 2020 Jan 26; cited 2020 May 31]; [about 8 screens]. Available from: https://www.uwhealth.org/health/topic/medicaltest/sputum-culture/hw5693.html#hw5725
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The medical information provided is for informational purposes only, and is not to be used as a substitute for professional medical advice, diagnosis or treatment. Please contact your health care provider with questions you may have regarding medical conditions or the interpretation of test results.

In the event of a medical emergency, call 911 immediately.