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Introduction ⬇

Normally, sugars are rapidly absorbed in the upper small intestine. However, if this is not the case, they remain in the intestine and cause osmotic diarrhea due to osmotic pressure of the unabsorbed sugar in the intestine, drawing fluid and electrolytes into the gut. The unabsorbed sugars are measured as reducing substances. Reducing substances that can be detected in the stool include glucose, fructose, lactose, galactose, and pentose. Carbohydrate malabsorption is a major cause of watery diarrhea and electrolyte imbalance seen in patients with short bowel syndrome. Idiopathic lactase deficiency is common in people with African and Asian ancestry.

The finding of elevated levels of reducing substances in the stool is abnormal and suggests carbohydrate malabsorption. A presumptive diagnosis of disaccharide intolerance can be made with an elevated reducing substance level along with an acidic (i.e., low) pH.

Normal Findings ⬆ ⬇

  1. Normal: less than 0.25 g/dL or less than 13.9 mmol/L reducing substances in stool

  2. Questionable: 0.25–0.50 g/dL or 13.9–27.8 mmol/L reducing substances in stool

Abnormal

More than 0.5 g/dL (or more than 27.8 mmol/L) reducing substances in stool

Procedure ⬆ ⬇

Collect a random, fresh stool specimen following the procedure for Collection and Transport of Random Specimens. Observe standard precautions and immediately deliver specimen to the laboratory.

Clinical Implications ⬆ ⬇

Elevated reducing substances in stool are found in the following conditions:

  1. Disaccharidase deficiency (intestinal)

  2. Short bowel syndrome (as a result of the surgical removal of the small intestine, there is a 
malabsorptive disorder)

  3. Idiopathic lactase deficiency, primary alactasia (enzyme deficiency leading to lactose intolerance)

  4. Carbohydrate malabsorption abnormalities due to:

    1. Celiac disease (celiac sprue)

    2. Viral gastroenteritis

Interventions ⬆ ⬇

Pretest Patient Care

  1. Explain purpose of test, procedure for stool collection, and interfering factors.

  2. Follow guidelines in Chapter 1 for safe, effective, informed pretest care.

Posttest Patient Care

  1. Review test results; report and record findings. Modify the nursing care plan as needed.

  2. Counsel the patient regarding abnormal findings; explain the need for further testing (lactose intolerance) and treatment (dietary therapy).

  3. Follow guidelines in Chapter 1 for safe, effective, informed posttest care.

Interfering Factors ⬆

  1. Bacterial fermentation of sugars may give falsely low results if the stool is not tested immediately.

  2. Newborns may normally have elevated results.

  3. Some drugs may cause malabsorption (e.g., neomycin, kanamycin, methotrexate).