Sputum Culture
A sputum culture is a diagnostic test used to identify bacteria or fungi in the lungs or airways that may be causing an infection or worsening a chronic respiratory condition.
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. 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. It contains cells from your immune system that help fight bacteria, fungi, or other foreign substances. The thickness of sputum helps trap foreign material, allowing cilia (tiny hairs) in the airways to push it through the mouth to be coughed out.
Sputum Colors and What They May Indicate
- Clear: Usually means no infection, though large amounts may indicate lung disease.
- White or gray: May be normal, but increased amounts may mean lung disease.
- Dark yellow or green: Often indicates a bacterial infection, such as pneumonia, or is common in people with cystic fibrosis.
- Black: Often seen in smokers or as a sign of black lung disease from long-term coal dust exposure.
- Brown or brown spots: May be a sign of old blood, cystic fibrosis, bacterial pneumonia, bacterial bronchitis, or exposure to dust or toxins.
- Pink: May indicate pulmonary edema, a condition involving excess fluid in the lungs often associated with heart failure.
- Red: May be an early sign of lung cancer or a pulmonary embolism. Seek immediate medical attention if you cough up red or bloody sputum.
What is it used for?
A sputum culture is most often used to:
- Find and diagnose bacteria or fungi causing lung or airway infections.
- Monitor if a chronic lung illness has worsened.
- Determine if treatment for a lung or airway infection is working.
- Diagnose conditions such as pneumonia, tuberculosis, and bronchiectasis.
This test is often performed alongside a Gram stain to help identify the specific type of infection. It is generally not used if a viral infection is suspected.
Why do I need a sputum culture?
You may need this test if you exhibit symptoms of pneumonia or other serious respiratory infections, including:
- Cough producing significant sputum
- Fever and chills
- Shortness of breath
- Chest pain during deep breathing or coughing
- Fatigue
- Confusion (especially in older adults)
What happens during a sputum culture?
Your provider needs a sample of your sputum. The process may include:
- Rinsing your mouth with water.
- Breathing deeply and coughing into a special cup.
- Chest tapping to help loosen mucus.
- Breathing in a salty mist to stimulate coughing.
- Bronchoscopy: If you cannot produce enough sputum, a provider may perform this procedure using a thin, lighted tube with a camera to collect a sample directly from the airway while you are relaxed and numbed.
Will I need to do anything to prepare for the test?
The test is often scheduled in the morning. You may be encouraged to drink extra water the night before. You may be asked to fast for one or two hours before the test, or up to twelve hours if you are undergoing a bronchoscopy. Inform your provider about all medications you take, as antibiotics can affect test results.
Are there any risks to the test?
There is no risk to providing a sputum sample. If you undergo a bronchoscopy, your throat may be sore, and it may take a few hours before you can cough normally or eat and drink.
What do the results mean?
Results typically take a few days to a few weeks depending on the bacteria being tested. Normal results mean no harmful bacteria or fungi were found. Not normal results may indicate an infection like pneumonia, bronchitis, or tuberculosis, or a flare-up of a chronic condition like cystic fibrosis or COPD.