A reference interval study of urinary lactulose excretion: a useful test of intestinal permeability in adults

Measurement of lactulose excretion in urine following oral ingestion is used as a noninvasive method of assessing small intestinal permeability. The aim of this study was to determine the adult reference interval of urinary lactulose excretion following oral administration. Thirty seven volunteers (mean age 37.3 +/- 15 years) with no history of gastrointestinal disease were recruited as study subjects. All subjects were fasted overnight (10 hours), emptied their bladders and then drank a 50-mL solution containing 15 mL of Duphalac (10 g lactulose) and 35 mL flavoured water. Urine was collected for six hours in a bottle. Comparisons were made for 37 samples. In adults, the mean urinary lactulose concentration was 0.58 +/- 0.39 mmol/L. This study determined the adult reference range for lactulose excreted in the urine, using a sensitive quantitative assay based on hydrolysing lactulose and enzymatically assaying fructose, one of the component monosaccharides.