Sputum Culture - Understand the Test & Your Results

What is a sputum culture?
A sputum culture is a test that checks for bacteria or another type of germ that may be causing a respiratory tract infection (an infection in your lungs or airways). 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, sputum can settle in your lungs, and you may also cough it up
Sputum is not the same as spit or saliva. Sputum contains cells from your immune system that help fight 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 check if a chronic illness has become worse. This helps your health care provider determine the best treatment. Sputum colors can include:
Clear. This usually means you don't have an infection, 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.
Black. 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.
Brown or brown spots. This may be a sign of old blood. This can happen if you have cystic fibrosis, bacterial pneumonia, bacterial bronchitis , or some other lung diseases. It can also be caused by breathing in dust or other brown materials or toxins.
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 heart failure .
Red. This may be an early sign of lung cancer. It may also be a sign of a pulmonary embolism (PE), 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, bacterial culture, respiratory
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 a lung or airway infection is working
Help to diagnose respiratory conditions such as pneumonia, tuberculosis , and bronchiectasis
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.
A sputum test is not usually used if your provider thinks you may have a viral infection.
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:
Cough which produces a lot of sputum
Fever
Chills
Shortness of breath
Chest pain that gets worse when you breathe deeply or cough
Fatigue
Confusion, especially in older people
Your provider may also order a sputum culture after an x-ray or other imaging tests show that you may have a lung infection. The sputum culture can help confirm this and determine the cause of the infection.
What happens during a sputum culture?
Your provider will need to get a sample of your sputum. During the test:
You may be asked to rinse your mouth out with water before the sample is taken.
Your provider will ask you to breathe deeply and then cough deeply into a special cup.
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 to 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 camera attached to a thin, lighted tube will be put through your mouth or nose and into your airway. This helps your provider see the inside of your lungs and airway.
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?
The test is often scheduled in the morning. To increase the amount of sputum, you may be encouraged to drink more water the night prior. You may also be asked not to eat for one or two hours before the test.
If you will be getting a bronchoscopy, you may be asked to fast (not eat or drink) for up to twelve hours before the test.
You may need to stop taking certain medicines before this test, so tell your provider about everything you take. Antibiotics may affect bacterial growth and the results of your sputum culture test. But don't stop taking any medicines unless your provider tells you to.
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.
If you had a bronchoscopy:
Your throat may feel sore after the procedure
It may take a few hours to be able to cough normally.
You will not be permitted to eat or drink until you can cough normally again.
What do the results mean?
Your sputum sample will be put in a dish with a special substance that allows bacteria to grow. It usually takes a few days to get the results of your sputum culture, but it may take weeks. How long it takes to get your results will depend on the type of bacteria that you are being tested for, since some types of bacteria take longer to grow in the lab
If your results were normal, it means that 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:
Pneumonia
Bronchitis
Tuberculosis
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 provider. To understand the results of your sputum culture, your provider will consider your symptoms, medical history, and the results of other tests.
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 tract (lungs and airways). Sputum (phlegm) is a type of mucus. Mucus can also be made elsewhere in the body, such as in the urinary or genital tract.
References
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