D-xylose absorption test: assesses the absorptive function of the upper small intestine
Because absorption of D-xylose in the intestine does not rely on the breakdown by pancreatic enzymes, a normal increase in urinary D-xylose excretion indicates a healthy intestinal mucosa. In conditions associated with damage to the intestinal mucosa, oral administration of D-xylose will result in increased fecal D-xylose excretion.
Hydrogen breath test: assess the intestinal absorption of individual carbohydrates