Stool Cultures: When They Are Ordered and Why

This Common, Noninvasive Test Is Used To Diagnose Digestive Disease

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When gastrointestinal symptoms such as diarrhea do not resolve on their own, your physician may want to look closer for an underlying cause. A stool culture may be part of a diagnostic work-up designed to do just that. 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 your digestive tract.


What Is It Used For?

A stool culture is used to detect pathogens that may be causing symptoms such as diarrhea, blood or mucus in the stool, abdominal pain, and nausea or vomiting. These gastrointestinal symptoms in turn may lead to dehydration and loss of electrolytes.

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 drinking water that has not been properly treated. If an infection is suspected to have occurred 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, 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 ordering the test will provide you with a sterile container to collect your stool. Care must be taken to ensure the stool is not mixed with urine or water from the toilet.

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.) Bacteria may be found with just one sample, but at times, up to three specimens from different bowel movements may be needed.

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. While many patients may feel embarassed 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. 

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. Most often, only one type of bacteria may be present, 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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