This test measures unabsorbed sugars in stool. It is used to evaluate the body’s ability to digest carbohydrates, or to absorb nutrients from food and drinks. Reducing substance determinations on stool specimens are useful in the detection of sugar intolerances. The presence of reducing substances is useful is the diagnosis of abnormalities in carbohydrate metabolism, i.e., sucrose and lactase. Stool tests are done if there are any of these symptoms diarrhea, poop with blood or mucus, stomach pain or mucus, Nausea, Fever, Throwing up etc.