8 Things a Stool Test Can Tell You About Your Health

If you're curious about gut health, understanding these differences helps you choose the right investigation. Some symptoms described as signs of unhealthy gut function can have several possible causes.

A stool test examines a small sample of faeces to investigate what is happening inside your digestive system. Depending on the test, it can detect infections, hidden blood, digestive abnormalities, or characteristics of your gut microbiome.

1. Which Bacteria Live in Your Gut

Your gut microbiome includes bacteria, archaea, viruses, and fungi. Unlike a stool routine test, advanced metagenomic sequencing examines microbial DNA in a stool sample.

• What it measures: Detectable microbial species and their estimated relative abundance, depending on the testing method.
• What it may reveal: Microorganisms such as Bifidobacterium, some species of which help break down dietary carbohydrates.
• What it cannot prove: That one particular bacterium is beneficial, harmful or responsible for your symptoms.

A 2025 scientific review highlights why researchers cannot define one universally ideal microbiome.

Explore our guide to what stool microbiome tests measure.

2. How Diverse Your Gut Microbiome Is

Think of your microbiome as an ecosystem containing different microorganisms. Diversity can be informative, but higher diversity does not always mean better health.

• What it measures: Species richness, or the number of different microorganisms, and evenness, or how evenly they are distributed.
• What it may reveal: How your microbial community compares with an appropriate reference population.
• What it cannot prove: Whether your microbiome is healthy based on a single diversity score.

A 2024 review published in Gut explains why microbial diversity must be interpreted alongside other factors.

For everyday context, read our five indicators of digestive wellbeing.

3. Whether Your Body Is Digesting Food Properly

Persistent diarrhoea, greasy stools or unexplained weight loss may indicate problems with digestion or nutrient absorption.

Different tests investigate different aspects:

• Faecal elastase test: Helps assess pancreatic enzyme production.
• Faecal fat test: Evaluates fat loss through stool when malabsorption is suspected.
• Microbiome test: May identify microbial genes associated with processing carbohydrates, proteins, and fats, but cannot directly measure your digestive enzyme activity.

The American Gastroenterological Association's 2023 guidance recommends faecal elastase as an initial investigation when pancreatic insufficiency is suspected.

Your everyday bowel habits also provide useful clues. A healthy stool is generally brown, soft, and easy to pass. A stool colour chart and the Bristol stool chart can help you describe changes, while tracking bowel movement frequency provides additional context.

For practical advice, explore the guide to improving digestion after 40.

4. If Harmful Microorganisms Are Present

Certain bacteria, viruses and parasites can cause gastrointestinal infections.

These may lead to diarrhoea, abdominal discomfort, fever or other symptoms.

• What it measures: Stool cultures, parasite examinations and molecular tests look for specific infectious organisms.
• What it may detect: Depending on the test, pathogens such as Salmonella, Giardia or Clostridioides difficile.
• What it cannot prove: Finding a potentially harmful organism in a general microbiome profile does not automatically establish an active infection.

A 2024 IDSA/ASM laboratory guideline recommends selecting infection tests according to symptoms, severity and clinical context.

5. Whether There Are Signs of Gut Inflammation

Inflammation is part of your body's immune response. However, persistent intestinal inflammation may require medical investigation.

• What it measures: Faecal calprotectin is a specific marker associated with intestinal inflammation. A stool routine test may also report pus cells in stool, which are white blood cells.
• What it may reveal: Elevated calprotectin can help clinicians investigate inflammatory bowel disease, including Crohn's disease and ulcerative colitis.
• What it cannot prove: A raised result cannot identify the underlying condition. Finding pus cells in stool also does not establish the cause of diarrhoea.

A 2023 meta-analysis involving 17 studies evaluated faecal calprotectin's usefulness in distinguishing inflammatory bowel disease from irritable bowel syndrome.

6. Whether There Is Hidden Blood in Your Stool

Blood is not always visible during a bowel movement.

A faecal immunochemical test (FIT) can detect small amounts of human blood in stool.

• What it measures: Hidden blood that may indicate bleeding within the digestive tract.
• Possible causes: Haemorrhoids, intestinal inflammation, polyps or colorectal cancer.
• What it cannot prove: A positive result does not mean you have cancer, and a negative result does not exclude every gastrointestinal condition.

Even a healthy stool in appearance may contain hidden blood.

A 2024 systematic review of 37 studies found FIT useful for investigating suspected colorectal cancer, while emphasising the need for follow-up when symptoms persist despite a negative result.

7. What Your Gut Microbes May Be Capable of Producing

Gut microorganisms have genes involved in processing food and producing compounds that support normal physiological processes.

Advanced metagenomic testing can explore some of these genetic pathways.

• Short-chain fatty acids: Certain microbes ferment dietary fibre to produce compounds such as butyrate, which provides energy for cells lining the colon.
• Vitamin biosynthesis: Some microbial genes are associated with producing B vitamins and other compounds.
• Bile acid metabolism: Microbial pathways can influence how bile acids are transformed within the intestine.

A 2024 scientific review explains the role of short-chain fatty acids in intestinal physiology.

Learn about food-based approaches in our probiotics, prebiotics and synbiotics guide.

8. How Your Gut Microbiome Relates to Overall Health

Your gut microbiome interacts with several systems throughout your body.

Researchers are studying its relationship with metabolism, immune function and communication between the gut and brain.

• Gut–brain interactions: Microbial metabolites and other signals may participate in communication between the digestive and nervous systems.
• Metabolic processes: Microbial pathways are associated with fibre fermentation, bile acid metabolism and other functions.
• Immune interactions: Gut microorganisms interact with immune cells and influence signalling pathways involved in immune regulation.

A 2025 review in Nature Reviews Microbiology examines communication between gut microorganisms and the brain.

However, these associations do not prove that a microbiome test can diagnose diabetes, liver disease, depression or other conditions.

Stool Test vs Gut Microbiome Test: Which One Should You Choose?

Both examine stool, but they answer different questions.

Explore our microbiome testing vs stool testing guide for more insight.

A 2025 international expert consensus highlighted that although gut microbiome tests can reveal information about microbial composition, their routine use for clinical diagnosis and treatment decisions remains limited by insufficient evidence.

Which Stool Test Should You Choose?

The right test depends on the question you want answered, not the number of parameters listed on a report.

• Persistent diarrhoea, fever or suspected parasites - A stool routine test or targeted infection testing may be appropriate, depending on your symptoms and clinical advice.
• Unexplained bleeding or bowel changes - Seek medical assessment. FIT, endoscopy or other investigations may be recommended.
• Greasy stools or suspected inflammation -  Your clinician may consider faecal elastase, faecal calprotectin or another targeted test.
• Interested in your microbial ecosystem - A microbiome test can provide exploratory information about microbial composition and genetic potential.

Our Decode Biome Gut Microbiome Test uses metagenomic sequencing to profile microbial communities and offers nutrition-focused reporting and guidance.

However, it is not intended to replace clinical investigations for infection, bleeding or inflammation.

How Does Your Lifestyle Affect Your Stool?

Your daily habits can influence stool consistency, frequency, and overall gut health.

Simple ways to support regular bowel movements include:

• Eat more fibre: Include vegetables, fruits, whole grains, and legumes.
• Stay hydrated: Adequate fluids help keep stools softer.
• Move regularly: Physical activity may support bowel regularity.
• Track changes: Notice persistent differences in your usual bowel patterns.

When Should You Seek Medical Advice?

Pay attention to persistent or unusual changes in your bowel habits.

• Consult a clinician: If you experience persistent diarrhoea, unexplained bowel changes, weight loss, abdominal pain, increased mucus, or pale stools.
• Seek urgent medical care: For heavy bleeding, black tarry stools with concerning symptoms, fainting, or severe dehydration.
• Collect samples correctly: Use your laboratory's clean container, avoid contamination with urine or toilet water, and follow the collection and delivery instructions.

Don't Flush Away the Clues

Your stool can tell you more about your digestive health than you might realise. Changes in colour, consistency or frequency may be temporary, but persistent or unusual patterns deserve attention.

A stool routine test can help identify certain abnormalities, although it cannot explain every digestive symptom. Pay attention to your usual bowel habits, maintain a fibre-rich diet, stay hydrated and seek medical advice when something feels consistently different. 

The next time you notice a change, don't simply flush it away. Understanding what's normal for your body can help you recognise warning signs and make more informed decisions about your gut health.

FAQs

1. What Are Bad Signs in Stool?

Blood, black tarry stool, persistent pale stool, prolonged diarrhoea, or unexplained changes in bowel habits deserve assessment.

2. Does Stool Size Change With Age?

It can vary with diet, hydration, and medicines, but persistent unexplained narrowing is not simply a normal sign of ageing.

3. What Does Healthy Stool Look Like?

Usually brown, soft, and easy to pass, commonly Bristol types 3–4.

Disclaimer: This article is for educational purposes only and is not a substitute for medical advice. Consult a qualified clinician about persistent symptoms or abnormal results.