A 41 year old patient presented with chronic diarrhea for 3 months. A d-xylose absorption test was ordered to look for
Carbohydrate malabsorption due to mucosal disease
Carbohydrate malabsorption due to chronic pancreatitis
Fat malabsorption due to mucosal disease
Fat malabsorption due to chronic pancreatitis
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
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