Evaluation of a triple sugar test of colonic permeability in humans

Conventional dual sugar tests of intestinal permeability assess only the stomach and small intestine. A novel triple sugar method of assessing colonic permeability has recently been described in animals. This utilizes the non-fermented sweetener sucralose, in addition to conventional sugars. It has been postulated that this test enables the simultaneous assessment of small-intestinal and colonic barrier function in humans. The aim of this study was to evaluate the triple sugar test using healthy volunteers and ileostomists.

Twenty-one healthy volunteers and 18 ileostomists underwent the triple sugar test. After an overnight fast, subjects drank a solution containing lactulose (5 g), rhamnose (1 g) and sucralose (5 g). Urine was collected for 0-5 h and 5-19 h. Urinary sugars were quantified using HPLC, and 5 and 24-h excretion calculated. Nineteen control subjects and 16 ileostomists also underwent a 51Cr-EDTA permeability test. Permeability data were presented as medians (IQR), and differences between groups analysed with Mann-Whitney U-tests.

Lactulose excretion and the 5-h lactulose/rhamnose (L/R) ratio were similar in controls and ileostomists [L/R ratio 0.024 (0.022-0.034) vs. 0.025 (0.022-0.035), P = 0.955]. Twenty-four hours excretion of sucralose was significantly higher in control subjects compared with ileostomists [1.41% (1.17-1.68) vs. 0.96% (0.64-1.2), P = 0.003]. The same pattern was seen with 51Cr-EDTA [2.73% (2.06-3.76) vs. 2.06% (1.55-2.71), P = 0.037] and with lactulose [0.52% (0.42-0.60) vs. 0.25% (0.16-0.35), P = 0.002].

Both sucralose and 51Cr-EDTA underwent significant colonic absorption. A significant amount of lactulose also appeared to be absorbed in the colon. This unexpected finding requires further study.