Stool Reducing substances

Evaluate disaccharidase deficiencies; determine if disaccharides are present in excessive amounts; screen for possible carbohydrate metabolism abnormalities.

Normally, sugars are rapidly absorbed in the upper small intestine. If not, they remain present in the intestine and undergo fermentation by bacteria to produce lactic acid. Resultant stool therefore may be acidic (a stool pH of < 6 is suggestive of sugar malabsorption). The unabsorbed sugar is measured as reducing substances.

Positive reducing substances should be followed up with carbohydrate chromatography to identify and quantify carbohydrates present.

This test is more useful for small infants than in older children and adults, who rarely have diarrhea from sugar intolerance; if they do, complete fermentation of sugar occurs in the colon, and reducing substances may not be present in the stool.