What is the primary purpose of the D-xylose test?

The primary purpose of the D-xylose test is to diagnose carbohydrate malabsorption. D-xylose is a simple sugar that does not require the action of pancreatic enzymes for absorption. When administered orally, D-xylose is absorbed in the small intestine, and its level in the urine or blood can indicate whether malabsorption is occurring. If the levels of D-xylose are low in urine or blood, it suggests that there may be a problem with the small intestine, potentially indicating conditions such as celiac disease or Crohn's disease, where the absorption of nutrients is impaired.

In contrast, evaluating gastric pH is not the focus of the D-xylose test, as it primarily assesses absorption in the small intestine rather than the acidity in the stomach. Similarly, assessing lactose tolerance typically involves a different test, such as the lactose tolerance test or hydrogen breath test, which specifically measures the body's ability to digest lactose. Lastly, while intestinal permeability might seem related, the D-xylose test specifically identifies issues with absorption rather than providing a direct measurement of permeability itself.