A 41 year old patient presented with chronic diarrhoea for 3 months. A d-xylose absorption test was ordered to look for:
**Core Concept**
The d-xylose absorption test evaluates carbohydrate malabsorption, specifically the ability of the small intestine to absorb d-xylose, a monosaccharide. It is primarily used to detect small intestinal mucosal dysfunction, such as in celiac disease or other conditions affecting intestinal villi integrity.
**Why the Correct Answer is Right**
D-xylose is absorbed in the small intestine via active transport in the mucosa. If absorption is impaired, it indicates mucosal disease (e.g., celiac disease, Crohn’s disease) affecting the intestinal lining. Unlike fat malabsorption, which is assessed by fat-soluble vitamin deficiency or stool fat tests, d-xylose testing is specific for carbohydrate malabsorption due to mucosal damage. Chronic pancreatitis does not typically cause d-xylose malabsorption because pancreatic enzymes are not directly involved in d-xylose digestion.
**Why Each Wrong Option is Incorrect**
Option B: Chronic pancreatitis primarily causes fat malabsorption due to insufficient lipase, not carbohydrate malabsorption. D-xylose absorption is not impaired in pancreatitis.
Option C: Fat malabsorption is assessed by fecal fat testing or fat-soluble vitamin deficiencies, not d-xylose. D-xylose is a carbohydrate, not a fat.
Option D: Chronic pancreatitis causes fat malabsorption, not carbohydrate malabsorption. D-xylose test is not relevant to pancreatic enzyme deficiency.
**Clinical Pearl / High-Yield Fact**
D-xylose absorption test is a specific screening tool for small intestinal mucosal disease; a negative result rules out carbohydrate malabsorption, but a positive result suggests mucosal injury. It is rarely used today due to better imaging and serological tests, but remains a classic exam topic.
✓ Correct Answer: A. Carbohydrate malabsorption due to mucosal disease