Xylose Tolerance Test (Fasting + Two-hour Blood Without Five-hour Urine-Adult)

Evaluate possible enterogenous malabsorption syndromes; testfor functional integrity of the jejunum Xylose is a pentose found naturally occurring in certain fruits such as plums. It is not normally found in significant concentrations in blood or urine thereby rendering the duodenojejunal absorption of d-xylose a usefulmechanism to assess the integrity of the gastrointestinal mucosa. d-Xylose is passively absorbed by the small bowel with some 30% to 40% of the ingested dose rapidly excreted in the urine. Absorption into the blood is evaluated at specific time intervals with intestinal malabsorption being indicatedby low absorption values. Low values would likewise be seen in celiac diseases, tropical spure, Crohn disease, immunoglobulin deficiency, pellagra, ascariasis, blind loop syndrome, radiation enteritis, surgical bowel resection, vomiting, delayed gastric emptying, inadequate hydration, decreased circulation, intrinsic renal disease, thyroid disease, ascites, and increased intestinal motility from anycause. The d-xylose absorption test may be of some help in distinguishing pancreatic insufficiency from jejunal malabsorption. Essentially normal d-xylose absorption valueswill be obtained in malabsorption values due to pancreatic insufficiency, whereas low blood values will be obtained in jejunal malabsorption. Urine values for xylose excretion are useful in determining renal insufficiency. Diminished excretion of d-xylose could be indicative of renal insufficiency, thereby invalidating the blood xylose absorption results. Low urine xylose valuescould also be attributed to incomplete collection or urinaryretention.

This test was developed, and its performance characteristics determined, by LabCorp. It has not been cleared or approved by the Food and Drug Administration.