A sputum culture, or sputum test, is a test that detects bacteria, fungi or other germs in your lungs or airways. Healthcare providers often use sputum cultures to diagnose respiratory infections and diseases such as pneumonia and tuberculosis. Sputum is a thick type of mucus produced in your lungs.
A sputum culture is a medical test that looks for bacteria and other germs to help diagnose an infection in your lungs or airways (respiratory tract). Healthcare providers frequently use sputum cultures when diagnosing and following up with people who have serious respiratory illnesses such as pneumonia and tuberculosis. They don’t usually use sputum tests if they suspect a viral infection. They only use them if they suspect you may have a bacterial or fungal infection. Another name for a sputum culture is a sputum test.
Sputum is a thick kind of mucus made in your lungs. Chronic illnesses and infections in your lungs or airways can make you cough up sputum. Another name for sputum is phlegm.
Sputum isn’t the same as saliva or spit. Sputum contains cells from your immune system that help fight the bacteria or other germs in your lungs or airways. The thickness of the sputum helps trap the germs. Tiny hairs in your airways called cilia push the sputum through to your mouth so you can cough it out.
Healthcare providers perform sputum cultures to help find out if there’s an infection in your lungs or airways and what’s causing it. Providers use the test to diagnose, plan treatment and monitor health conditions.
Providers use sputum tests to help diagnose infections that may be affecting your lungs and airways. Bacteria, fungi and other germs can cause these conditions. A sputum culture can help determine which type of germ is causing the infection. Common conditions that sputum cultures help diagnose include:
Your healthcare provider may use a sputum test to help create a treatment plan for lung conditions. Knowing what’s causing an infection allows your provider to choose the most appropriate treatment option for you. In some instances, your provider may use a sputum culture for susceptibility testing. Susceptibility testing evaluates how germs in a sputum sample react when they’re exposed to certain drugs.
Your healthcare provider can use sputum testing to track your condition over a period of time. A sputum test helps your provider figure out if an infection has improved or worsened. This tells them whether a prescribed treatment has been effective.
Your healthcare provider may request a sputum culture if you have symptoms of a serious lung infection, such as pneumonia. Symptoms of lung infections may include:
If you have symptoms of a respiratory infection, your provider will likely request a chest X-ray or CT scan before ordering a sputum culture. If imaging tests show a lung infection, your provider may order a sputum culture to determine what’s causing it.
Your provider may also request a sputum culture if:
To perform a sputum culture, your healthcare provider will collect a sample of your sputum. They need to get enough sputum to work with at the laboratory. The most common and least invasive way for you to provide this sample is by coughing deeply and then spitting into a cup. If you can’t produce enough sputum through this method, your provider may use a more invasive procedure called a bronchoscopy. They’ll insert a flexible tube through your mouth or nose into your lungs to collect a sample directly.
After your provider collects a sample of sputum, they send it to a laboratory. In the lab, a pathologist places the sample in a special dish containing a material called a medium. If there are bacteria or other germs in the sample, the medium enables them to grow. After a day or so, the pathologist checks the sample to evaluate the amount and type of germs in the dish.
If you’ll be coughing and spitting into a cup, your healthcare provider may tell you to drink a lot of water the night before the sputum culture. This will enable you to cough up more mucus. Your provider may ask you not to eat for one to two hours before the sputum test. They’ll usually schedule your test for some time in the morning when your sputum is more concentrated.
If you’ll be having a bronchoscopy, your provider will ask you to fast for up to 12 hours before the test. Fasting means not eating or drinking anything other than water. Your provider may also change the medications you’re taking before the test, especially if you take blood thinners. You should arrange for transportation after the procedure.
What you can expect during the test depends on the method of collection.
Before your healthcare provider collects a sample of sputum, you may need to rinse your mouth out with water. Then, your provider will instruct you to take a few deep breaths. After that, they’ll have you forcefully cough every couple of minutes until you can bring up mucus that you spit into a cup. You may need to repeat this process several times until you produce enough phlegm.
To help bring up phlegm, your provider may:
If you still can’t produce enough sputum, your healthcare provider may perform a bronchoscopy. First, they’ll give you medicine to help you relax. Then, they’ll give you a numbing medicine (anesthesia) so you won’t feel any pain.
Your provider will insert a thin, lighted tube through your nose or mouth, into your lungs and airways. The tube has a small camera on it so your provider can see images of your lungs and airways. They’ll collect a sputum sample from your airway using a small brush or suction attached to the tube.
During a bronchoscopy, you may feel some pressure from the tube or experience some difficulty breathing. But the procedure shouldn’t be painful because the anesthesia should numb the area.
After a cough and spit test, you may continue to cough for a while, which may cause some discomfort.
After a bronchoscopy, it may take two to three hours to regain your normal ability to cough. You won’t be able to eat or drink anything during this time. In addition, your throat may feel irritated or scratchy for a few days.
There are no risks to getting a sputum test.
Side effects from the cough and spit method may include slight discomfort from repeated coughing. If you’ve had a bronchoscopy, your throat may feel sore for a few days following the procedure.
Pathologists typically report the results of a sputum culture test as normal (negative) or abnormal (positive):
An abnormal result may support a diagnosis of a lung condition, such as pneumonia or tuberculosis, that’s associated with an underlying infection. However, the results of a sputum test aren’t a definitive diagnosis. Your healthcare provider must carefully interpret the results. They’ll review the results along with other factors, including:
In the laboratory, the bacteria or other germs need time to grow. A pathologist normally won’t analyze the culture for at least 24 hours. Because of this, your sputum culture test results may take a few days. Your healthcare provider will contact you to go over the results of your test. You may receive the results in person, over the phone or through an electronic health record.
If your results are abnormal, you may have some kind of bacterial or fungal infection. Your healthcare provider may need to perform more tests to determine which kind of infection you have. You may also be having a flare-up of a chronic condition, such as chronic obstructive pulmonary disease (COPD) or cystic fibrosis (CF). Your healthcare provider will reach out to you about your results.
If your provider had to perform a bronchoscopy, your throat may feel irritated or sore for a few days after the procedure. If this soreness persists or you have any other side effects from the procedure, contact your provider.
A note from Cleveland Clinic
Healthcare providers perform sputum cultures to determine if you have an infection in your lungs or airways. Coughing into a cup doesn’t sound too stressful, but getting a bronchoscopy might. Your provider will help you relax and make you as comfortable as possible no matter the method of collection. If you have questions about whether you need a sputum culture, talk with your healthcare provider.
Last reviewed by a Cleveland Clinic medical professional on 08/04/2023.
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