Sputum Culture
Reviewed
Also called: respiratory culture, bacterial sputum culture, routine sputum culture, bacterial culture, respiratory
A sputum culture is a laboratory test that checks for bacteria or fungi that may be causing a respiratory tract infection in your lungs or airways. It helps diagnose infections such as pneumonia, tuberculosis, and bronchitis, and can monitor chronic lung conditions.
Specimen: Sputum (phlegm, not saliva)
Why this test may be ordered
- Find and diagnose bacteria or fungi causing a lung or airway infection
- See if a chronic lung illness has worsened
- Check if treatment for a lung infection is working
- Help diagnose respiratory conditions such as pneumonia, tuberculosis, and bronchiectasis
Preparation and collection
The test is often scheduled in the morning. You may be encouraged to drink more water the night before. You may be asked not to eat for 1–2 hours before the test. If you are having a bronchoscopy, you may need to fast for up to 12 hours. Tell your provider about all medicines you take, including antibiotics, but do not stop taking any medicine unless your provider tells you to.
You will be asked to breathe deeply and cough deeply into a special cup. If you have trouble coughing up enough sputum, you may be asked to breathe in a salty mist, or a bronchoscopy may be performed to collect a sample using a small brush or suction.
There is no risk to providing a sputum sample into a container. If a bronchoscopy is needed, your throat may feel sore afterward, and it may take a few hours before you can cough normally. You will not be allowed to eat or drink until you can cough normally again.
Understanding results
Your sputum sample is placed in a dish with a substance that allows bacteria to grow. Results are typically reported as normal (no harmful bacteria or fungi) or abnormal (harmful bacteria or fungi detected, or a flare-up of a chronic condition).
- Normal: No harmful bacteria or fungi were found in your sputum. Limitation: A normal result does not rule out all infections; your provider will consider your symptoms and other tests. Next step: routine
- Abnormal: Harmful bacteria or fungi were found, or a chronic condition (such as cystic fibrosis or COPD) may have worsened. This may indicate a bacterial or fungal infection. Limitation: Your provider may need to do more tests to identify the specific infection. Antibiotics can affect results. Next step: prompt
- Antibiotics may affect bacterial growth and test results.
- Results may take a few days to weeks depending on the type of bacteria being tested.
- This test is not usually used for viral infections.
What to do next
Your healthcare provider will interpret your results based on your symptoms, medical history, and other tests. If your results are abnormal, additional tests may be needed to identify the specific infection.
- What do my sputum culture results mean in combination with my symptoms?
- Do I need any other tests to confirm the diagnosis?
- Should I stop taking any of my medicines before this test?