Stool Reducing Substances
This stool test detects unabsorbed sugars in the gut that can cause diarrhoea and digestive discomfort. It is commonly used to assess carbohydrate malabsorption.
Turnaround time
5 days
Biomarkers count
1
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Details about Stool Reducing Substances
What is the Stool Reducing Substances Test?
The Stool Reducing Substances Test measures the presence of unabsorbed sugars in a stool sample. These sugars—such as lactose, glucose, fructose, or galactose—are normally absorbed in the small intestine, and their presence in stool suggests impaired digestion or absorption.
The test works by identifying substances that chemically “reduce” copper salts, indicating excess carbohydrates reaching the colon. It is particularly useful when symptoms suggest sugar intolerance or malabsorption rather than infection or inflammation.
This test is frequently used in infants and children but is also relevant for adults with unexplained diarrhoea, bloating, or suspected malabsorption syndromes.
Why do I need a Stool Reducing Substances Test?
When carbohydrates are not properly absorbed, they pass into the colon where they ferment, drawing water into the bowel and producing gas. This process can cause persistent gastrointestinal symptoms that are often misattributed to infections or food sensitivity without objective testing.
You may benefit from this test if you experience:
- Chronic or watery diarrhoea
- Excessive gas or bloating
- Abdominal cramping
- Acidic or foul-smelling stools
- Poor weight gain or weight loss
- Symptoms after consuming milk or sugary foods
- Digestive symptoms with normal infection screens
This test is especially helpful in assessing lactose intolerance, disaccharidase deficiencies, post-infectious malabsorption, and some paediatric digestive disorders.
Benefits of the test
- Identifies carbohydrate malabsorption
Detects unabsorbed sugars that contribute to diarrhoea and bloating. - Supports intolerance investigations
Helps assess lactose and other sugar intolerances. - Explains persistent diarrhoea
Useful when infection and inflammation tests are normal. - Non-invasive assessment
Requires only a stool sample, no blood draw needed. - Useful in children and infants
Commonly used when feeding-related symptoms occur. - Guides dietary review
Results support targeted nutritional evaluation. - Complements other stool tests
Works alongside parasite, culture, or calprotectin testing. - Reduces unnecessary investigations
Helps narrow down digestive causes efficiently.
Step-by-step: How we offer testing
Clinic-based testing (UK-wide)
- Choose your nearest UK clinic
- Receive a stool collection kit with instructions
- Collect the sample at home
- Return the sample for laboratory analysis
- Results are issued once testing is complete
Home or hotel service (+£60, UK-wide)
- Order your test with home support
- Collection kit provided with clear instructions
- No clinic visit required
- Ideal for convenience, children, or reduced mobility
Your results explained
Negative / not detected (normal)
- No significant reducing substances found
- UK standard: Negative
- Suggests normal carbohydrate absorption
Trace / borderline
- Small amounts of reducing substances present
- UK standard: Trace positive
- May indicate mild or transient malabsorption
Positive (elevated)
- Significant reducing substances detected
- UK standard: Positive
- Indicates carbohydrate malabsorption and requires clinical correlation
How It Works
Simple steps to get your results
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Choose your test online and book in seconds. Select your preferred clinic location or home visit option.
Visit or Test at Home
Attend one of our UK or London clinics, arrange a home nurse visit, or use a finger-prick kit where available.
Get Your Results
Your sample is analysed by accredited UK laboratories, with secure results delivered directly to you.
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WhatsApp UsHow to Prepare for Your Test
Follow these guidelines for accurate results
Sample Timing
Where possible, attend your blood test between 7am and 12pm. Please wait until any short-term illness or infection has fully resolved before testing. Avoid intense exercise for 24–48 hours beforehand, as this can affect certain markers.
Fasting & Hydration
Fasting is not always required, but some tests may recommend it. If fasting is advised, avoid food for 8–12 hours before your appointment and drink water only. Stay well hydrated, as this helps with sample collection and accuracy.
Medications & Supplements
Continue prescribed medications unless advised otherwise by your clinician. Avoid vitamin, mineral, or biotin supplements for at least 24–48 hours before your test, as these can interfere with results. If you are unsure about any medication or supplement, please let us know before your appointment.
Hormones & Menstrual Cycle
For hormone-related tests, timing within your menstrual cycle may be important. If relevant, follow any specific guidance provided on your test page.
If you have any questions or special circumstances, our team is happy to advise before your appointment.