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

1. Identifies carbohydrate malabsorption
   Detects unabsorbed sugars that contribute to diarrhoea and bloating.
2. Supports intolerance investigations
   Helps assess lactose and other sugar intolerances.
3. Explains persistent diarrhoea
   Useful when infection and inflammation tests are normal.
4. Non-invasive assessment
   Requires only a stool sample, no blood draw needed.
5. Useful in children and infants
   Commonly used when feeding-related symptoms occur.
6. Guides dietary review
   Results support targeted nutritional evaluation.
7. Complements other stool tests
   Works alongside parasite, culture, or calprotectin testing.
8. 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