The d-xylose absorption test helps differentiate malabsorption due to intestinal mucosa from pancreatic insufficiency because:

• A. d-Xylose is mostly absorbed in the stomach and excreted via kidney in unaltered form
• B. d-Xylose is mostly altered in the small intestine and metabolized by the liver
• C. d-Xylose is mostly absorbed, not typically found in the blood, unaltered in the small intestine, and excreted unaltered via the kidney
• D. None of the above describe why the d-xylose test is useful

Answer: (C)

The test hinges on how d-xylose behaves in the gut and body. d-xylose is absorbed in the proximal small intestine by a simple diffusion process that does not require pancreatic enzymes or extensive intestinal processing, and it is not significantly metabolized by the liver. After absorption, it remains largely unchanged and is eliminated by the kidneys into the urine. So, the amount of d-xylose that shows up in the urine after an oral dose reflects the absorptive capacity of the small intestine, not pancreatic digestive function.

That’s why the statement describing d-xylose as being mostly absorbed, remaining unaltered as it passes through the small intestine, and being excreted unchanged in the urine is the best reflection of how the test differentiates mucosal malabsorption from pancreatic insufficiency. If the mucosa is damaged, absorption drops and urinary excretion falls; if the mucosa is intact (even with pancreatic insufficiency), absorption and urinary excretion stay normal. The other descriptions misstate where absorption occurs or how d-xylose is handled by the body.