Stool Cultures: When They Are Ordered & Why

This Common, Noninvasive Stool Test Is Used to Help Diagnose Digestive Disease

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Some digestive problems, such as diarrhea, may go away on their own, but when they do not, a trip to the doctor is in order. A physician will want to do some tests to see if there is an underlying cause for symptoms such as diarrhea, abdominal pain, and nausea or vomiting. A stool culture may be part of a number of tests that a doctor will order that are designed to find out what is causing all the symptoms.

Used used to examine stool for harmful bacteria, parasites, or an overgrowth of the “helpful” bacteria that resides in the intestine, a stool culture can be an important glimpse into the health of the digestive tract. Thankfully, a stool test is noninvasive and, as tests go, fairly easy.

What Is It Used For?

A stool culture is used to detect pathogens (such as bacteria or parasites) that may be causing symptoms such as diarrhea, blood or mucus in the stool, abdominal pain, and nausea or vomiting. These gastrointestinal symptoms, if they go on too long, could lead to dehydration and loss of electrolytes. Most people can drink enough water or other fluids to keep up, but sometimes the amount of water and salt being lost through diarrhea or vomiting is more than a person can take in.

Pathogenic bacteria could be ingested, such as from contaminated water, undercooked eggs or meat, or unpasteurized milk.

This may happen during travel to a developing nation, but it may also occur at home from poor food handling or from drinking water that has not been properly treated. If an infection with a bacteria is suspected to have occurred while eating out at a restaurant (food poisoning), the doctor or hospital will make a report to the local health department.

This test may be used in a standard work-up for ulcerative colitis, Crohn’s disease, or irritable bowel syndrome. Prolonged diarrhea can be a symptom of all three conditions (as well as others), but it could also be caused by a parasitic infection.

How Do I Prepare for a Stool Culture?

There are usually no preparations required for a stool culture; stool is simply collected in a sterile container and taken to a lab for testing.

The physician or other healthcare provider that orders the test will provide a sterile container to collect stool (along with any other items needed, such as disposable gloves). Care must be taken to ensure the stool is not mixed with urine or with water from the toilet. A healthcare provider may give directions on the best way to take the sample. In the case of diarrhea, wearing a disposable glove and holding the sample cup under the bottom while using the toilet may work well to collect the stool.

The sample should be taken immediately to the lab because it must be put into a nutrient solution. (If not taken immediately, the sample should be refrigerated or kept cold.) Bacteria may be found with just one sample, but at times, up to three specimens from different bowel movements may be needed for testing.

How Is a Stool Sample Performed?

After the stool is placed in the culture, it may take two to three days for any bacteria that is in the stool to grow. These bacteria can then be isolated and examined under a microscope so that they may be identified.

The stool may also be tested for parasites or eggs. This is done by examining a smear of the sample under a microscope.

What Are the Risks?

This test is safe and painless and relatively private if one collects the stool while using the bathroom alone. While many patients may feel embarrassed or uncomfortable presenting their stool to a lab, it is important to keep in mind that receiving stool samples is a standard part of the job for lab technicians and just business as usual for them.

Putting the sample in a bag, such as a brown paper bag, to carry it to the lab can help.

Is Any Follow-up Necessary?

Call your doctor in a few days for the results. If a pathogen is found, the test result is positive or “isolated,” treatment may be necessary. The treatment needed will depend on the type of bacteria that was found. Most often, only one type of bacteria may be in the stool, but in some cases there may be multiple pathogens. If no pathogen is found, a result or negative or “not isolated,” more tests may be needed to find the cause of the symptoms.

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