Wallach's Interpretation of Diagnostic Tests: Pathways to Arriving at a Clinical Diagnosis (1307 page)

XYLOSE ABSORPTION TEST

   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