Test Catalog

Interpretive Handbook

Test 83255 :
Reducing Substance, Feces

Clinical Information Discusses physiology, pathophysiology, and general clinical aspects, as they relate to a laboratory test

Sugars (eg, glucose, galactose, fructose, maltose, lactose, and pentose) are characterized as reducing substances based on their ability to reduce cupric ions to cuprous ions.


Fecal reducing substances may be increased in carbohydrate malabsorption syndromes.

Useful For Suggests clinical disorders or settings where the test may be helpful

Diagnosing intestinal malabsorption in children


Assisting in the differentiation between osmotic and nonosmotic diarrhea


Screening test for:

-Diarrhea from disaccharidase deficiencies, (eg, lactase deficiency)

-Monosaccharide malabsorption

Interpretation Provides information to assist in interpretation of the test results

Negative: negative

Normal: <0.25 g/dL (trace)

Suspicious: 0.25 to 0.50 g/dL (grade 1)

Abnormal: >0.50 g/dL (grade 2-4)

Cautions Discusses conditions that may cause diagnostic confusion, including improper specimen collection and handling, inappropriate test selection, and interfering substances

A number of other compounds also are capable of reducing cupric ions to cuprous ions and can cause false-positives.


Ambient transport temperatures result in growth of bacteria. Bacteria consume reducing substances, which can result in false-negative results, so ambient specimens are rejected.


This test has poor sensitivity for oligosaccharides and poor sensitivity from diaper stools because fluid is reabsorbed into the diaper. Testing of only the solid portion of the stool will give a falsely-low reading since the liquid portion of the stool contains the water-soluble sugars.


Possible interferences include: salicylates, penicillin, choral hydrate, menthol, phenol, streptomycin, para-aminosalicylic acid, isoniazid, ascorbic acid, cephalosporins, and probenecid.

Reference Values Describes reference intervals and additional information for interpretation of test results. May include intervals based on age and sex when appropriate. Intervals are Mayo-derived, unless otherwise designated. If an interpretive report is provided, the reference value field will state this.

Negative or trace

Clinical References Provides recommendations for further in-depth reading of a clinical nature

Todd S: Archives of disease in childhood: differentiation of osmotic and secretory diarrhea by stool carbohydrate and osmolar measurements. In Clinical Diagnosis and Management by Laboratory Methods. Vol 77. 20th edition. Edited by JB Henry, FR Davey, CJ Herman, et al. Philadelphia, Saunders, 2001, pp 201-205