A stool culture is a test on a stool sample to find germs (such as bacteria or a fungus) that can cause an infection. A sample of stool 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.
Depending on what your stool is being tested for, you may only need to collect one stool sample. Or you may need several stool samples over a period of days.
Why It Is Done
A stool culture is done to:
- Find the cause of symptoms. It can help explain symptoms such as severe or bloody diarrhea or an increased amount of gas. It can also help find the cause of nausea, vomiting, loss of appetite, bloating, belly pain and cramping, and fever.
- Find and identify certain types of organisms that are causing infections or diseases. These include food poisoning, inflammation of the large intestine (colitis), cholera, and typhoid.
- Identify a person who may not have any symptoms of disease but who carries bacteria that can spread infection to others. This person is called a carrier. A person who is a carrier and who handles food is likely to infect others.
- Find out if treatment for an infection has worked as it should.
How To Prepare
You do not need to do anything special to prepare for this test.
Talk to your doctor about any concerns you have about the need for the test, its risks, how it will be done, or what the results will mean. To help you understand the importance of this test, fill out the medical test information form(What is a PDF document?).
How It Is Done
Stool samples can be collected at home. Or you may need to go to your doctor's office, a medical clinic, or the hospital. If you collect the samples at home, you may be given a special container.
You may need to collect more than one sample. Follow the same steps for each sample.
To collect the sample:
- Urinate before you collect the stool. That way, you won't get any urine in the stool sample. Do not urinate while you pass the stool.
- Put on gloves before handling your stool. Stool can contain germs that spread infection. Wash your hands after you take off your gloves.
- Pass stool (but no urine) into a dry container. You may be given a plastic basin that you can place under the toilet seat to catch the stool.
- Either solid or liquid stool can be collected.
- If you have diarrhea, a large plastic bag taped to the toilet seat may make the collection process easier. The bag is then placed in a plastic container.
- Do not collect the sample from the toilet bowl.
- Do not mix toilet paper, water, or soap with the sample.
- Place the lid on the container. Label it with your name, your doctor's name, and the date the stool was collected. If you need more than one sample, use a separate container for each sample. Collect a sample only once a day unless your doctor gives you other directions.
Take the sample to your doctor's office or the lab as soon as you can. You may need to take your sample to the lab within a certain time, usually within 30 minutes or less of collecting it. Tell your doctor if you think you may have trouble getting the sample to the lab on time.
Samples from babies and young children may be taken from diapers (if the stool does not have urine mixed with it). Or a narrow tube may be put into the baby's rectum while you hold the baby on your lap.
Sometimes a stool sample is collected using a rectal swab. The swab is inserted into the rectum, rotated gently, and then pulled out. It is placed in a clean, dry container and sent to the lab right away.
How It Feels
Most people do not feel pain when they collect a stool sample.
If your doctor collects the stool sample using a cotton swab, you may feel some pressure or discomfort as the cotton swab is inserted into your rectum.
There is no chance for problems while collecting a stool sample.
Be sure to wear gloves when you collect the sample. Wash your hands before and after you collect the sample. This will help protect you from spreading an infection.
A stool culture is done to find bacteria, viruses, parasites, or fungi that may be causing an infection.
Stool culture test results usually take 2 to 3 days. But some cultures for fungus and parasites may take weeks to get results.
No disease-causing bacteria, fungi, parasites, or viruses are present or grow in the culture.
If bacteria are found in the culture, sensitivity testing may be done to help choose the best treatment.
Your stool also may be looked at under a microscope to check for parasites such as Giardia.
What Affects the Test
You may not be able to have the test, or the results may not be helpful, if:
- You recently used antibiotics, medicine (such as bismuth) to control diarrhea, enemas, or laxatives.
- You recently had X-ray tests using a contrast material containing barium.
- Your stool sample is mixed with urine.
- You do not have a large enough sample.
- You did not get the stool sample to the lab for testing quickly enough.
What To Think About
- You may have an infection even if your stool culture test is normal.
- A stool sample may be checked for parasites such as pinworms, roundworms, tapeworms, and Giardia.
- A stool sample can also be checked for:
- A stool analysis is a series of tests done on a sample of stool to help diagnose certain conditions that affect the digestive tract. These conditions include infection, poor absorption, and cancer. To learn more, see the topic Stool Analysis.
Other Works Consulted
Chernecky CC, Berger BJ (2008). Laboratory Tests and Diagnostic Procedures, 5th ed. St. Louis: Saunders.
Fischbach FT, Dunning MB III, eds. (2009). Manual of Laboratory and Diagnostic Tests, 8th ed. Philadelphia: Lippincott Williams and Wilkins.
Pagana KD, Pagana TJ (2010). Mosby’s Manual of Diagnostic and Laboratory Tests, 4th ed. St. Louis: Mosby Elsevier.
Primary Medical ReviewerAdam Husney, MD - Family Medicine
E. Gregory Thompson, MD - Internal Medicine
Specialist Medical ReviewerJerome B. Simon, MD, FRCPC, FACP - Gastroenterology
Current as ofAugust 21, 2015