Sputum is a thick fluid made in the lungs and in the airways leading to the lungs. A sputum culture is a test to find germs (such as bacteria or a fungus) that can cause an infection. A sample of sputum is added to a substance that promotes the growth of germs. If no germs grow, the culture is negative. If germs that can cause infection grow, the culture is positive. The type of germ may be identified using a microscope or chemical tests. Sometimes other tests are done to find the right medicine for treating the infection. This is called sensitivity testing.
You may be asked to cough to provide the sputum sample. Some people can't cough deeply enough to produce a sample. They can breathe in a special mist to help them cough.
Why It Is Done
A sputum culture is done to:
- Find bacteria or fungi that are causing an infection of the lungs or the airways leading to the lungs. Examples include pneumonia and tuberculosis. Symptoms of a lung infection may include having a hard time breathing, pain when breathing, or a cough that produces bloody or greenish brown sputum.
- Find the best antibiotic to treat the infection. (This is called sensitivity testing.)
- See if treatment is working.
How To Prepare
Do not use mouthwash before you collect your sputum sample. Some types of mouthwash can kill bacteria and could affect your results.
If bronchoscopy will be used to collect your sputum sample, your doctor will tell you how soon before the test to stop eating and drinking. Follow the instructions exactly about when to stop eating and drinking. If you don't, your surgery may be canceled. If your doctor told you to take your medicines on the day of surgery, take them with only a sip of water.
Tell your doctor if you have recently taken antibiotics.
How It Is Done
In most cases, the sputum sample is collected early in the morning before you eat or drink anything. In some cases, three or more morning samples may be needed. (This is often done if you may have tuberculosis.)