Stool reducing substances (stool sugar) test
Quick answer: This test checks stool for sugars that the gut has not absorbed. It is mostly used in babies and children with diarrhoea to look for sugar intolerance, such as lactose intolerance.
- SampleStool
- TakesA few minutes to collect the sample
- Before the testA fresh, liquid part of the stool is needed, as results change if the sample is kept too long.
How the test is done
- 1You collect a fresh liquid or soft stool sample
- 2For babies, staff may collect from a nappy lined with plastic
- 3The lab mixes the stool with water and a reagent tablet or solution
- 4A colour change shows whether unabsorbed sugars are present
What your results can mean
Reading your report
Results are usually reported as negative or as a level; your doctor will read them with your child's symptoms.
If the result is outside the usual range
Reducing sugars in stool can point to sugar intolerance, such as lactose intolerance after a gut infection, or other problems absorbing sugar. A negative result makes these less likely.
Who usually has this test
Babies and young children with watery diarrhoea, especially after milk feeds.
Risks and aftercare
There are no risks for your child; keep up fluids while diarrhoea lasts.
Names and options
Also called: stool sugar, reducing sugars stool
Options
- Reducing substances, stool
- Sugar, stool
Listed by the hospital as
- REDUCING SUBSTANCES, STOOL
- SUGAR, STOOL
Questions about this test
Why must the stool sample be liquid?
The sugars are in the watery part of the stool. Nappies soak up this liquid, so staff may line the nappy with plastic to collect it.
Can a gut infection cause a positive result?
Yes, a bout of diarrhoea can damage the gut lining for a while and make it harder to digest lactose. This usually settles with time.
Should I change my baby's feeds after a positive result?
Do not change feeds on your own. Discuss the result with your child's doctor, who will advise based on the full picture.
Related tests
Tamara Hospital & IVF Centre, Rajajinagar
34/3, 10th Cross Road, opp. Vardhaka Sardar Patel School, 1st N Block, 2nd Stage, Rajajinagar, Bengaluru 560010
The hospital is open 24 hours. Call before you come to check the timing for your scan or sample collection.
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This page explains each test in general terms so you know what to expect. It is not medical advice: your doctor decides which tests you need and what your results mean. Reference ranges differ between laboratories. Updated 4 November 2026.