Stool Sample – Test, Procedure and Clinical Relevance
A stool sample is a laboratory test of fecal matter used to detect diseases of the digestive tract. It aids in diagnosing infections, inflammation, and bowel conditions.
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A stool sample is a laboratory test of fecal matter used to detect diseases of the digestive tract. It aids in diagnosing infections, inflammation, and bowel conditions.
What Is a Stool Sample?
A stool sample (also called a stool test or fecal analysis) is a diagnostic procedure in which a small amount of stool is examined in a laboratory for various components. It is one of the most common and important tests in gastroenterology and general medicine. The procedure is painless, non-invasive, and provides valuable information about the health of the gastrointestinal tract.
When Is a Stool Sample Collected?
A stool sample may be recommended or ordered for a variety of medical reasons. Common indications include:
- Persistent diarrhea or constipation
- Blood in the stool (visible or hidden)
- Suspected gastrointestinal infection (e.g., bacterial, viral, or parasitic)
- Investigation of abdominal pain or bloating
- Suspected chronic inflammatory bowel disease such as Crohn's disease or ulcerative colitis
- Colorectal cancer screening (detection of occult blood)
- Follow-up after antibiotic-associated colitis (e.g., Clostridioides difficile infection)
- Return from travel to regions with a high infection risk
How Is a Stool Sample Collected?
The patient collects the stool sample at home. A special container with a small spoon or spatula is provided by the doctor or pharmacy. The stool is deposited into a clean receptacle and a small amount is transferred into the sample container. Depending on the clinical question, one or more samples may be required on consecutive days.
Important Collection Tips
- The stool should not be contaminated with urine or toilet water.
- Some tests require prompt submission of the sample (within a few hours).
- Certain dietary restrictions may apply before specific tests (e.g., the fecal occult blood test).
- For suspected parasitic infections, samples from three consecutive days may be needed.
What Is Analyzed in a Stool Sample?
Depending on the clinical question, different parameters can be measured in a stool sample:
Microbiological Analysis
This involves testing for bacteria, viruses, and parasites (e.g., amoebas or Giardia). Common pathogens detected include Salmonella, Campylobacter, norovirus, and Giardia lamblia.
Fecal Occult Blood Test (FOBT / iFOBT)
This test detects hidden (occult) blood in the stool that is not visible to the naked eye. It is routinely used for colorectal cancer screening and is part of standard preventive care for adults over 50 in many countries.
Calprotectin
Calprotectin is an inflammatory marker. Elevated levels indicate intestinal inflammation and help distinguish between organic bowel diseases (e.g., Crohn's disease) and functional disorders (e.g., irritable bowel syndrome).
Elastase
Pancreatic elastase in the stool reflects the function of the pancreas. Low levels may indicate exocrine pancreatic insufficiency, a condition in which the pancreas does not produce enough digestive enzymes.
pH and Fat Content
The pH value of the stool and its fat content (assessed for steatorrhea) are helpful in diagnosing digestive and malabsorption disorders.
How Are Results Interpreted?
Stool sample results must always be evaluated in the context of clinical symptoms and additional findings. A positive blood test does not automatically mean colorectal cancer, but it is an important indicator that warrants further investigation, such as a colonoscopy. Elevated calprotectin levels also require follow-up. The treating physician will discuss the results and initiate the next steps as needed.
Risks and Limitations
Collecting a stool sample is completely risk-free. Potential sources of error include:
- Improper storage or delayed submission of the sample
- Contamination with urine or water
- Use of certain medications (e.g., aspirin, iron supplements) before testing
- False-negative results on occult blood tests due to intermittent bleeding
References
- World Health Organization (WHO): Guidelines for the Control of Shigellosis. Geneva, 2005. Available at: https://www.who.int
- Rex DK et al. - Colorectal Cancer Screening: Recommendations for Physicians and Patients from the U.S. Multi-Society Task Force on Colorectal Cancer. Gastroenterology. 2017;153(1):307-323.
- Roseth AG et al. - Assessment of the neutrophil dominating protein calprotectin in feces. Scandinavian Journal of Gastroenterology. 1992;27(9):793-798.
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