Diagnosis: D-Xylose test
• In the D-xylose test, the patient is given an oral dose of D-xylose after an overnight fast, and then urinary excretion of this molecule is monitored.
• The purpose of this test is to differentiate enteric causes of malabsorption (e.g., ileal dysfunction) from pancreatic causes (e.g., tumor, fibrosis, surgery).
• In patients with malabsorption caused by pancreatic insufficiency (or in a healthy patient), the urinary level of D-xylose should be elevated after the bolus because this sugar does not require pancreatic enzymes for absorption.
• In patients with malabsorption caused by enteric pathology, very little to no D-xylose will be absorbed; therefore, it will not be excreted in the urine.
• Any renal impairment will affect clearance of D-xylose and, therefore, interferes with proper interpretation of the test results.
