A 41 year old patient presented with chronic diarrhea for 3 months. A d-xylose absorption test was ordered to look for

URINARY d-XYLOSE TESTThe urinary d-xylose test for carbohydrate absorption provides an assessment of proximal small-intestinal mucosal function. d-Xylose, a pentose, is absorbed almost exclusively in the proximal small intestine. The d-xylose test is usually performed by administering 25 g of d-xylose and collecting urine for 5 h. An abnormal test (excretion of <4.5 g) primarily reflects duodenal/jejunal mucosal disease.The d-xylose test can also be abnormal in patients with blind loop syndrome (as a consequence primarily of an abnormal intestinal mucosa) and, as a false-positive study, in patients with large collections of fluid in a third space (i.e., ascites, pleural fluid).The ease of obtaining a mucosal biopsy of the small intestine by endoscopy and the false-negative rate of the d-xylose test has led to its diminished use. When a small-intestinal mucosal disease is suspected, a small-intestinal mucosal biopsy should be performed.Ref: Harrison; 19th edition; Page no: 1938