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Subject: Xylose Absorption Test
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d-xylose is a monosaccharide that does not require digestion by pancreatic enzymes or bile acids prior to absorption. In this test, 25 g of d-xylose is given orally and blood xylose levels are measured at 1 and 3 hours later and urinary excretion of xylose is measured for 5 hours. Abnormal d-xylose test suggests a mucosal problem as the cause of malabsorption.
Serum: ≥25 mg/dL (adult, 1 hour, 25-g dose, normal renal function)
Urine: ≥4 g/5 hours (5-hour urine collection in adults >12 years [25-g dose])
Diagnose conditions that presents with malabsorption due to defects in the integrity of gastrointestinal mucosa.
Malabsorption syndromes, such as Celiac or Crohn disease
Small intestine bacterial overgrowth
d-xylose results can be normal in malabsorption syndromes caused by pancreatic insufficiency.
False-positives can occur with decreased renal function, dehydration/ hypovolemia, surgical blind loops, decreased gastric emptying, vomiting.
Patients should not eat foods containing high levels of pentose, including fruits, jams, jellies, and pastries for 24 hours prior to test.
Low values can also be caused by inflammation of the lining of the intestine, short bowel syndrome, and infection with parasites, like giardiasis or hookworm.
Blood d-xylose levels are generally considered more reliable than urine levels in children younger than 12 years old.