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Sputum Culture

Does this test have other names?


What is this test?

This test helps find out what is causing your respiratory tract infection. Sputum is the mucus that settles in the lower airways of your lungs when you have an infection or a chronic illness. It’s also called phlegm.

A lung infection such as pneumonia can cause you to cough up sputum. Other conditions, such as bronchiectasis and COPD (chronic obstructive pulmonary disease), can also cause coughing and make it hard to breathe. This test helps your healthcare provider find out if the buildup of sputum in your lungs is caused by bacteria, fungi, or another germ. Knowing the cause of your infection can help your healthcare provider decide on the right treatment for you.

Why do I need this test?

You may need this test if your healthcare provider thinks that you have a lung infection such as pneumonia, especially if you're coughing up a lot of sputum.

You may also have this test if you have severe pneumonia and are admitted to the hospital.

What other tests might I have along with this test?

You may also need an X-ray, blood culture, sputum Gram stain, or urine antigen test to find the source of your infection.

If your healthcare provider thinks you may have a chronic lung condition, you may have other tests, including:

  • CT scan

  • Pulmonary function test to see how well your lungs work

  • Complete blood count (CBC)

  • Erythrocyte sedimentation rate (ESR) and C-reactive protein tests to look for inflammation

What do my test results mean?

Test results may vary depending on your age, gender, health history, and other things. Your test results may be different depending on the lab used. They may not mean you have a problem. Ask your healthcare provider what your test results mean for you.

A negative result means that you don't have a lung infection. A positive result means bacteria were found. But it may not pinpoint the exact cause of your condition. Some bacteria are normally found in the lungs and cause no problems. Your healthcare provider may have to do other tests to a make a diagnosis.

How is this test done?

The test is done with a sputum sample from deep inside your lungs. You may need to rinse your mouth with water first. You'll then be asked to cough up enough mucus for a culture sample to be taken. If you can't cough up enough fluid, your healthcare provider may use a bronchoscope to get a sample for testing. This tool is a narrow, flexible tube with a light on it. The tube is put in through your nose or mouth and down your throat through your windpipe (trachea) and into the tubes leading to your lungs. You will likely get some medicine to help you relax during the procedure.

Does this test pose any risks?

This test has no known risks.

What might affect my test results?

Taking antibiotics can cause a false-negative result. That's because these medicines may kill the bacteria causing the problem. It's best to have a sputum culture before starting any antibiotic medicines.

How do I prepare for the test?

You may need to stop taking antibiotics before the test. You may also need to not eat or drink for 1 to 2 hours before the test or longer if your healthcare provider plans to use a bronchoscope to get the sample.

Be sure your healthcare provider knows about all the medicines, herbs, vitamins, and supplements you are taking. This includes medicines that don’t need a prescription and any illegal drugs you may use.

Online Medical Reviewer: Chad Haldeman-Englert MD
Online Medical Reviewer: Raymond Turley Jr PA-C
Online Medical Reviewer: Tara Novick BSN MSN
Date Last Reviewed: 9/1/2022
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