The xylose absorption test may be ordered to help determine whether a person is absorbing carbohydrates normally and to distinguish between malabsorption disorders caused by insufficient pancreatic enzymes or bile and those due to intestinal dysfunction.
It may be ordered as a follow-up test if other test results, such as fecal fat, suggest malabsorption but do not reveal its cause.
This is not a routine test. Its use and availability has declined over time. Major health organizations, including the American Gastroenterology Association, the World Gastroenterology Organization, and the British Society of Gastroenterology, do not include this test in their guidelines for evaluating possible malabsorption.
With the xylose absorption testing procedure, high blood and urine levels of xylose are normal. They indicate good xylose absorption by the intestines. This suggests that the tested person's symptoms are likely due to another cause, such as pancreatic or bile insufficiency.
High blood but low urine levels may be seen in someone with kidney dysfunction. In this case, it is the blood levels that will be used to evaluate the individual for malabsorption.
Low levels of blood and urine xylose indicate poor absorption. A variety of conditions that affect digestion and absorption may cause decreased xylose levels. These may include bacterial overgrowth in the intestines, parasitic infections, a shortened bowel (such as from surgery) and celiac disease.
Depending upon a person's clinical situation, an abnormal xylose test may be followed by additional blood or stool tests to try to isolate the cause and/or by a small-bowel biopsy to look at intestinal cells.
This article was last reviewed on December 4, 2011. | This article was last modified on January 27, 2012.
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