Function tests

• Suspicion of malabsorption syndrome
• Suspicion of malfunctioning of the functional integrity of the upper small intestine

D-xylose given orally is actively absorbed in the proximal small intestine. Illnesses, which lead to a restriction of the absorbing intestinal surface in the proximal small intestine, show a pathologically decreased D-xylose excretion in the urine as well as decreased D-xylose concentration in the serum.

Xylose

2,4 ml sodium fluoride blood each, 15 min, 1 hour and 2 hours following xylose administration, 5 hours urine collection.

• Patient needs to be fasting (only for the first 2 hours of test), ask patient to empty urinary bladder. Taking of bloods prior to xylose administration to get the basal value.
• Oral administration of 25g D-xylose in 300 ml water or tea (children get

5 g/m2 body surface area in 100ml).

• Collect urine over a period of 5 hours. Again, in the first two hours have the patient drink the same amount of fluid as before.
• Taking of blood 1 hour and two hours after test commencement (children after 1 hour only).
• Measure urine volume after 5 hours and send 2,4 ml in a urine sample tube, stating the total urine amount.

Side effects:
Winds, diarrhea, nausea may occur

Normal findings:

Urination:

Adults: > 4 g/5 hours or 22 – 24 % of the administered xylose amount

Children: > 1,2 – 2,4 g/5 hours or 15 – 35 % of the administered xylose amount.

Blood levels:

Adults:

After 15 min: >15 mg/dl

After 1 hour: > 30 mg/dl

After 2 hours: > 30 mg/dl

Children:

After 1 hour: > 20 mg/dl

Malabsorption

A pathological decrease in D-xylose excretion in the urine and decreased D-xylose concentration in the serum indicate a dysfunctional absorption in the upper small intestine, i.e. a malabsorption in gluten sensitive enteropathy.

Most common cause:

Non-tropical sprue (Celiac disease)

Less common causes:

Amyloidosis, resection of the small intestine, bypass surgery, intestinal lymphoma, scleroderma, radioactivity-induced enteritis, malabsorption with mucous membrane destruction due to pharmaceutics (i.e. neomycin), Whipple’s disease, carcinoid syndrome, tropical sprue, Zollinger-Ellison syndrome.

Dysfunctions:

Pernicious anemia, medications: aspirin, phenformin or indomethacin, kidney insufficiency, ascites, cholestasis, bacterial overgrowth of the small intestine, chronic alcohol consumption.

Please note:

• The xylose test comes back normal in case of lactase deficiency (lactose intolerance) and chronic pancreatitis with pancreas insufficiency.
• In case of pathological results of xylose test, a biopsy of the small intestine is indicated.