Limitations of the usefulness of the d-xylose absorption test.

The results of the conventional 5-hour d-xylose absorption test were surveyed in 38 subjects with disease of the jejunal mucosa, giardiasis or bacterial overgrowth, or no small-bowel disorder. The test was in error in 20-40% of cases, depending on the disease category, and the error for the entire group was 30%. We conclude that the test yields little guidance for diagnosis or therapy of clinical problems and is superfluous when a jejunal biopsy can be obtained.