Reviewed by: HU Medical Review Board | Last reviewed: June 2016. | Last updated: May 2019
After using the Rome III criteria to assess a patient’s frequency of symptoms and how long they have been experiencing those symptoms, as well as ruling out other conditions through a physical exam, doctors may also use stool analysis in diagnosing irritable bowel syndrome (IBS). Stool analysis, also called a stool test, is used to determine if symptoms might be caused by an organic disorder of the colon, such as an infection or an inflammatory disease.1
Stool tests are usually performed in patients with liquid, loose, or diarrheal stool to determine if there is an infection or inflammation from IBS with diarrhea (IBS-D). The absence of diarrhea, such as in IBS with constipation (IBS-C), effectively excludes clinically significant inflammation or an infection.1
Stool ova and parasites exam
The stool ova and parasites exam is designed to look for eggs (ova) or adult parasites. Stool analysis for parasites can be useful in diagnosing IBS in patients with acute diarrhea – that which is less than 4 weeks in duration – but not in chronic diarrhea, which is characterized by more than 4 weeks in duration. Generally, IBS-D patients experience the chronic diarrhea.1,4
Stool gram stain
A stool gram stain, or feces Gram stain, is used to determine and identify the presence of bacteria in the stool. Bacteria may be present in an intestinal infection. The stool gram stain is generally used in diagnosing IBS in cases with acute diarrhea, those less than 4 weeks in duration.1,4
Additional stool tests
If a patient has symptoms that are characteristic of IBS-D, and results from blood tests are normal, stool analysis is not necessary. However, if there is concern that the symptoms may be caused by inflammatory bowel disease (IBD) and blood tests for celiac disease are negative, then stool analysis for fecal leukocytes and fecal calprotectin are often conducted.
- Fecal leukocytes is a test for the presence of white blood cells in the stool, which are usually not present in the absence of infection or inflammation.2
- Fecal calprotectin is a simple and non-invasive method for assessing a protein released by white blood cells, which frequently occurs in IBD.1,3
When diagnosing IBS, stool analysis is similar to the physical exam in that it rules out other potential causes for the symptoms the patient is experiencing. Because there is not a specific test that indicates a patient has IBS, stool tests are not always performed in the diagnosis of IBS.
How the stool tests are performed
To evaluate the stool, the patient must collect a stool sample. Because mixing the sample with urine, water or toilet tissue can cause an inaccurate test result, the sample is usually collected using a test kit with a special toilet tissue and container, or by catching the stool on plastic wrap that is placed over the toilet bowl, under the toilet seat. The healthcare provider’s office will provide you with instructions on when and how to submit a stool sample. The sample is then sent to a laboratory where stains and a microscope are used to identify the presence of bacteria or other components.