The D-xylose absorption or tolerance test is used for evaluating patients with possible malabsorption, especially if celiac disease (gluten sensitive enteropathy) is suspected. D-xylose is a pentose sugar with a molecular weight of 150.15 grams. It is passively absorbed from the small intestine (particularly the jejunum), with 30-40% of the absorbed amount excreted in the urine. Failure to excrete a certain amount of D-xylose in the urine is seen in enterogenous malabsorption; pancreatic enzymes are not required for D-xylose absorption. Patients with renal disease may show reduced urine excretion, and should also have plasma samples drawn at specified times during the test.