Stool Gram stain

Definition

A stool Gram stain is a laboratory test that uses different stains to detect and identify bacteria in a stool sample.

The Gram stain method is sometimes used to quickly diagnose bacterial infections.

How the Test is Performed

You will need to collect a stool sample.

There are many ways to collect the sample.

Do not mix urine, water, or toilet tissue with the sample.

For children wearing diapers:

Your health care provider will give you instructions on when and how to return the sample.

The sample is sent to a laboratory. A small amount is spread in a very thin layer on a glass slide. This is called a smear. A series of special stains are added to the sample. The lab team member looks at the stained smear under the microscope to check for bacteria. The color, size, and shape of the cells help identify the specific bacteria.

How the Test will Feel

A lab smear is painless and does not directly involve the person who is being tested.

There is no discomfort when a stool sample is collected at home because it only involves normal bowel functions.

Why the Test is Performed

Your provider may order this test to help diagnose an intestinal infection or illness, sometimes involving diarrhea.

Normal Results

A normal result means only normal or "friendly" bacteria were seen on the stained slide. Everyone has friendly bacteria in their intestines.

Normal value ranges may vary slightly among different laboratories. Talk to your provider about the meaning of your specific test results.

What Abnormal Results Mean

An abnormal result means that an intestinal infection may be present. Stool cultures and other tests can also help diagnose the cause of the infection.

Risks

There are no risks.


Review Date: 10/12/2018
Reviewed By: David C. Dugdale, III, MD, Professor of Medicine, Division of General Medicine, Department of Medicine, University of Washington School of Medicine, Seattle, WA. Also reviewed by David Zieve, MD, MHA, Medical Director, Brenda Conaway, Editorial Director, and the A.D.A.M. Editorial team.

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