Xylose Absorption Test

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Subject: Xylose Absorption Test

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Definition

  • 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.

  • Normal range:

    • 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])

Use

  • Diagnose conditions that presents with malabsorption due to defects in the integrity of gastrointestinal mucosa.

Interpretation

Increased In

  • NA.

Decreased In

  • Malabsorption syndromes, such as Celiac or Crohn disease

  • Small intestine bacterial overgrowth

  • Whipple disease

Limitations

  • 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.

 
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