A "stool examination for reducing substances test" is a laboratory test that analyzes a stool sample to detect the presence of unabsorbed sugars, also known as "reducing substances," which can indicate issues with carbohydrate absorption in the digestive system, often used to diagnose conditions like lactose intolerance or malabsorption syndromes; a positive result means the body is not properly absorbing sugars like glucose, fructose, lactose, and galactose in the stool sample.