Irritable bowel syndrome (IBS) is a common disorder affecting the large intestine. It can cause symptoms like abdominal pain, bloating, diarrhea, and constipation. IBS is diagnosed based on a person’s symptoms, but stool testing can provide additional information to support an IBS diagnosis.
A stool sample allows a doctor to check for signs of inflammation, infection, or other gastrointestinal conditions that may be causing a patient’s symptoms. It can also help monitor IBS and guide treatment decisions. Here is an overview of how a stool sample can indicate IBS:
What is examined in a stool sample?
Several aspects of a stool sample may be analyzed to look for clues related to IBS:
- Consistency – Stools may be loose, watery, or ribbon-like in IBS with diarrhea. They may also be hard and dry in IBS with constipation.
- Color – Stools often look normal brown in IBS, but can sometimes appear paler or grayish.
- Mucus – Increased mucus in stool, appearing like a clear jelly-like substance, can occur with IBS.
- Blood – A small amount of blood may be visible in stool with IBS due to sensitive intestinal tissues.
- Bacteria and parasites – Stool analysis helps rule out intestinal infections causing diarrhea.
- Fecal leukocytes – These white blood cells in stool indicate inflammation associated with diarrhea.
- Fecal fat – Poor absorption of fat can happen with chronic diarrhea.
Looking at these aspects of a stool sample can provide clues about symptoms of diarrhea, constipation, pain, and other signs that may be related to IBS.
How do stool sample results point to IBS?
There are no definitive diagnostic markers in a stool sample that confirm IBS. However, stool test results can support an IBS diagnosis by providing evidence such as:
- No signs of infection – Normal stool culture and parasites rules out infectious causes of diarrhea.
- No inflammation – Lack of blood, leukocytes, and fecal lactoferrin indicates no inflammatory bowel disease.
- No malabsorption – Normal fat absorption makes celiac disease unlikely.
- Changes matching symptoms – Loose stools in diarrhea or dry, hard stools in constipation correlate with IBS symptoms.
Essentially, stool sample findings that fail to indicate any gastrointestinal abnormality outside of changes associated with altered bowel habits and abdominal discomfort help point to IBS as the underlying cause.
When is a stool test done for IBS?
Doctors may order stool testing in IBS patients to:
- Help diagnose IBS – Stool tests can rule out other conditions with similar symptoms.
- Confirm suspected IBS relapse – New onset of diarrhea or constipation along with pain may warrant repeat stool analysis.
- Check for exacerbating factors – Stool testing can identify bacterial or parasitic infections triggering IBS flare-ups.
- Monitor IBS treatment – Repeat stool analysis can ensure treatments, like antibiotics for SIBO, are working.
- Screen for other diseases – Stool tests may be performed to screen for colon cancer and other diseases in high-risk patients.
Repeat stool testing is not needed in all IBS patients but may be done periodically to re-evaluate symptoms and check for other conditions that can develop over time.
Preparing for a Stool Sample Test
To get the most accurate results from a stool sample test, proper preparation is important:
Getting the Sample
The patient collects a stool sample at home following instructions from the doctor’s office or lab. Tips include:
- Pass stool directly into a clean collection container, not the toilet.
- Collect a sample from a bowel movement at its peak consistency and texture.
- Gather stool from multiple areas of the same bowel movement.
- Fill the container to the level (e.g. teaspoon) requested by the lab.
Storing and Transporting the Sample
Proper storage and transport ensures stool sample quality:
- Seal the container tightly to avoid leaking or contamination.
- Label the container with name, date of collection, and other info as directed.
- Refrigerate sample if not returning it within an hour.
- Return sample to the lab promptly within the requested timeframe.
- Keep sample cool en route by refrigerating or packing in ice.
- Avoid extremes of heat or freezing during storage and transport.
Following the storage, labeling, and transport guidelines provided for the stool sample ensures the lab can perform accurate testing.
Medications and Diet Prior to Sample Collection
Certain medications and diet factors can impact stool sample results:
- Stop taking laxatives, stool softeners, antacids, and some other drugs beforehand as instructed.
- Avoid barium tests and bismuth-containing medications like Pepto Bismol before collecting a sample.
- Follow any special diet (e.g. high fat) recommended by the doctor in the days leading up to the test.
- Avoid alcohol for 48 hours prior to collecting a stool sample.
Checking with the doctor about diet and medication restrictions ahead of time ensures the sample reflects the normal state of the stool rather than artifacts from medications, diet, or procedures.
Understanding Stool Sample Test Results
Various laboratory tests can be performed on a stool sample. Here is an overview of some common tests and what the results might indicate about IBS:
Stool culture
- Checks for growth of disease-causing bacteria like Salmonella, Shigella, Campylobacter, or E. coli O157.
- Negative culture without bacterial growth rules out infectious diarrhea, supporting IBS.
Ova and parasites exam
- Checks stool under a microscope for parasites like Giardia or Cryptosporidium or eggs from parasitic worms.
- No parasites seen supports IBS rather than parasitic infection causing diarrhea.
Fecal leukocytes
- Microscopic examination looking for increased white blood cells which indicate inflammation.
- Normal leukocytes counts make inflammatory bowel diseases like ulcerative colitis unlikely.
Fecal fat test
- Measures amount of fat in stool, with excess fat indicating malabsorption.
- Normal fat absorption makes celiac disease and other malabsorption problems unlikely.
Fecal calprotectin
- Tests level of protein indicating intestinal inflammation with high levels linking to inflammatory bowel disease.
- Normal calprotectin levels help exclude inflammatory causes of diarrhea.
Fecal lactoferrin
- Measures marker of intestinal inflammation with elevation seen in inflammatory bowel disease.
- Normal lactoferrin is consistent with IBS, not inflammatory diarrhea.
By reviewing the full panel of stool sample results, the doctor can determine if any findings point to an infectious, inflammatory, malabsorptive, or other cause of symptoms outside of IBS. Results consistent with IBS support this diagnosis while abnormal results can indicate other conditions to explore.
Conditions That Can Be Confused with IBS
Since IBS symptoms can mimic other gastrointestinal disorders, doctors must rule out the following conditions when evaluating stool samples:
Inflammatory Bowel Diseases
Inflammatory bowel diseases like Crohn’s disease and ulcerative colitis can cause diarrhea, abdominal pain, and other IBS-like symptoms. However, they produce inflammation and potentially blood, leukocytes, and elevated fecal biomarkers like calprotectin and lactoferrin detectable on stool analysis. Normal stool test results help exclude these conditions.
Infectious Diarrhea
Bacterial infections from Salmonella, Campylobacter, Shigella, or E. coli can trigger diarrhea mimicking IBS diarrhea. Parasitic infections by Giardia, Cryptosporidium, Blastocystis hominis, or Dientamoeba fragilis can also lead to persistent diarrhea and cramps. Stool cultures and O&P exams that fail to identify microbial causes of diarrhea rule out infectious diarrhea in favor of IBS.
Celiac Disease
Celiac disease often presents with diarrhea, bloating, and abdominal discomfort that may mimic IBS with diarrhea. However, celiac patients have an abnormal immune reaction to gluten that causes malabsorption and can lead to fatty stool noticeable on fecal fat testing. Normal fat absorption makes celiac disease unlikely.
Microscopic Colitis
Microscopic colitis, including lymphocytic colitis and collagenous colitis, often presents with chronic watery diarrhea and cramping. But microscopic examination of stool shows inflammatory cells and collagen deposits in the colon. The lack of these microscopic abnormalities can help exclude microscopic colitis as the cause of diarrhea.
Lactose Intolerance
Difficulty digesting lactose can cause diarrhea, bloating, and flatulence mimicking IBS. But stool testing shows acidic stool pH and possibly presence of undigested lactose in lactose intolerance. These specific findings are absent in IBS patients.
Careful testing for these and other conditions with overlapping symptoms is crucial to ensure IBS remains the most likely diagnosis after excluding identifiable organic diseases.
Benefits of Stool Testing for IBS Diagnosis
While no single stool test can definitively diagnose IBS, analyzing a stool sample offers benefits including:
- Supports IBS diagnosis by ruling out infections like C. diff, parasites, and other causes of diarrhea or abnormal stools.
- Provides clues about the subtype of IBS, such as loose stools pointing to IBS-D.
- Monitors for flare-ups, relapse, or worsening of symptoms based on changing stool findings.
- Helps assess the efficacy and impact of IBS treatments.
- Screens for other possible gastrointestinal conditions that may develop.
- Provides reassurance to patients that no serious diseases are being overlooked.
Stool testing gives doctors objective data to correlate with a patient’s subjective symptom reports. Combining stool sample results with a detailed history and clinical presentation optimizes the accuracy of diagnosing IBS.
Limitations of Stool Testing
While analyzing a stool sample can support an IBS diagnosis, there are limitations to consider:
- Stool findings alone cannot provide a definitive IBS diagnosis – the full clinical context must be considered.
- Normal stool test results do not absolutely rule out other gastrointestinal disorders.
- Abdominal pain, a hallmark IBS symptom, is not reflected in stool testing.
- repeat checks, diet, and other issues.
- Incomplete or incorrectly collected stool samples may provide inaccurate results.
- Some patients find collecting stool samples uncomfortable or embarrassing even with proper instructions.
Given these limitations, doctors must use their clinical judgement and synthesize stool sample findings with a patient’s full history and perspective to make an accurate IBS diagnosis.
Takeaways on Stool Testing for IBS Diagnosis
Key points to understand about using stool sample analysis in diagnosing IBS:
- Stool tests alone cannot definitively diagnose IBS but can support the diagnosis.
- Stool testing is often used to help rule out infection, inflammation, malabsorption, and other gastrointestinal disorders.
- Normal stool culture, O&P exam, fecal fat level, and other test results consistent with IBS help exclude alternate causes of diarrhea, constipation, and pain.
- Stool findings should correlate with the patient’s reported IBS symptoms.
- Proper stool sample collection, storage, transport, and knowing what factors may affect results are important.
- Doctors should interpret stool testing together with the full clinical presentation when diagnosing IBS.
While no single diagnostic test confirms IBS, stool sample analysis is one useful tool that can provide corroborating objective evidence supporting a symptom-based IBS diagnosis when integrated thoughtfully with the comprehensive clinical picture. Understanding how to collect and interpret stool testing provides valuable insights for managing patients.