Ans is A (Carbohydrate malabsorption due to mucosal disease) `The urinary D-xylose test for carbohydrate absorption provides an assessment of proximal small intestine mucosal function.' Urinary D-xylose test: Principle D-xylose is a `pentose. that is completely absorbed almost exclusively in the proximal small intestine and excreted subsequently in the urine. The level of excreted D-xylose in urine is estimated. Any decrease in its level in urine means abnormality in carbohydrate absorption in proximal intestine. Procedure & interpretation 25g D-xylose is given and urine is collected for 5 hrs. An excretion of < 4.5e primarily reflects the presence of duodenal /jejuna) mucosal disease.