A stool culture is done to identify bacteria
or viruses that may be causing an infection. Although more than 50 different
kinds of bacteria normally live in the
intestines, large numbers of abnormal bacteria,
parasites can grow in the intestines and cause
infections and diseases.
For a stool culture, a stool sample is
collected in a clean container and placed under conditions that allow bacteria
or other organisms to grow. The type of infection is identified by noting the
appearance of the growth, by performing chemical tests on the stool sample, and
by looking at the sample under a microscope.
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, such as severe or
bloody diarrhea, an increased amount of gas, nausea, vomiting, loss of
appetite, bloating, abdominal pain and cramping, and fever, especially if you drank untreated water from a stream or lake or have been traveling outside of the country.
and identify certain types of bacteria, viruses, or fungi that are
causing infections or diseases, such as
food poisoning, inflammation of the large intestine
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 been effective.
How To Prepare
No special preparation is required
before having this test. Tell your doctor if you have recently taken
antibiotics, traveled out of the country, or
had a recent test with
contrast material, such as a barium swallow or a barium enema.
Talk to your doctor
about any concerns you have regarding 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,
in your doctor's office, at a medical clinic, or at 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 procedure
for each sample.
Collect the sample as follows:
Urinate before collecting the stool so that you
do not get any urine in the stool sample. Do not urinate while passing the
Put on gloves before handling your stool. Stool can contain
germs that spread infection.
Wash your hands after you remove your gloves.
Pass stool (but no
urine) into a dry container. You may be given a plastic basin that can be
placed under the toilet seat to catch the stool.
Either solid or liquid stool can be
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
If you are constipated, you may be given a small
Do not collect the sample from the toilet
Do not mix toilet paper, water, or soap with the sample.
Place the lid on the container and label it with
your name, your doctor's name, and the date the stool was collected. If you are
collecting more than one sample, use one container for each sample, and collect
a sample only once a day unless your doctor gives you other directions.
Take the sealed container to your doctor's office or the
laboratory as soon as possible. You may need to deliver your sample to the lab
within a certain time. Tell your doctor if you think you may have trouble
getting the sample to the lab on time.
You may need to collect
several stool samples over 7 to 10 days if you have digestive symptoms after
traveling outside the country.
Samples from babies and young
children may be collected from diapers (if the stool is not contaminated with
urine) or from a small-diameter glass tube inserted into the baby's rectum
while the baby is held on an adult's lap.
Sometimes a stool sample
is collected using a rectal swab that contains a preservative. The swab is
inserted into the rectum, rotated gently, and then withdrawn. It is placed in a
clean, dry container and sent to the lab right away.
How It Feels
Collecting a stool sample does not
normally cause any discomfort.
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 and 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 identify
bacteria, viruses, or fungi that may be causing an infection. Stool
culture test results usually take 2 to 3 days. But some cultures for fungus may take weeks to get results.
No disease-causing (pathogenic) bacteria, fungi, or viruses are present or grow in the culture.
Bacteria (such as
salmonella, shigella, campylobacter, certain types of
Escherichia coli[E. coli], or
Yersinia enterocolitica) grow in the culture. Fungi such as yeast are found in the stool.
If bacteria are found in the culture,
sensitivity testing may be done to help choose the
The stool also may be examined under a microscope to look for parasites such as Giardia.
What Affects the Test
Reasons you may not be able to
have the test or why the results may not be helpful include:
Recent use of antibiotics, medicine (such as
bismuth) to control diarrhea, enemas, or laxatives.
Not getting 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.
testing helps your doctor choose the best treatment for the specific disease or
A stool sample may be tested for
parasites such as pinworms, roundworms, tapeworms and
the protozoan Giardia that causes
giardiasis. The parasites or their eggs can often be
seen during an examination of the stool sample under a microscope.
(toxins) produced by some types of bacteria.
A stool analysis is a series of tests done on a
sample of stool to help diagnose certain conditions affecting the digestive
tract, including infection, poor absorption, or cancer. To learn more,
see the topic
Other Works Consulted
Chernecky CC, Berger BJ (2008). Laboratory Tests and Diagnostic Procedures, 5th ed. St. Louis:
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 Reviewer
Adam Husney, MD - Family Medicine
Specialist Medical Reviewer
Jerome B. Simon, MD, FRCPC, FACP - Gastroenterology
How this information was developed to help you make better health decisions.