Xylose Tolerance Test (Fasting, One-, Two-, Three-, Four-, and Five-hour Blood + Five-hour Urine)/ Xylose Tolerance Test (Fasting, One-, Two-, Three-, Four-, and Five-hour Blood Without Five-hour Urine)
Diagnose intestinal malabsorption syndromes
Plasma and urine/ Plasma
2 mL plasma (each specimen) and 10 mL aliquot of five-hour urine/ 2 mL (each specimen)
0.6 mL plasma (each specimen) and 0.5 mL aliquot of five-hour urine /1 mL (each specimen)
Gray-top (sodium fluoride) tube and plastic urine container
Patient must fast a minimum of eight hours prior to administration of d-xylose. Pediatric patients (younger than nine years of age) should fast only four hours. No restriction on water. Weigh patient for proper dosage of d-xylose. Patient must remain in supine position for duration of the test except during urine collection. Patient should refrain from foods rich in pentose (fruits, preserves, and grains) for a 24-hour period prior to the test. Weight-based dosage of d-xylose for oral administration: 0.5 g/kg body weight up to a maximum of 25 g. Dissolved in water 10% (w/v) with a maximum of 250 mL. Patient should drink eight ounces (250 mL) of water after d-xylose administration and another eight ounces after one hour. Record total five-hour urine volume and send aliquot. Record total on the test request form.
Plasma: Draw fasting sample, administer d-xylose dose (see Patient Preparation), and obtain one-, two-, three-, four-, and five-hour samples postdose. Centrifuge and separate plasma from cells immediately. Indicate time drawn (ie, “fasting,” “one-hour,” etc) on each plasma tube submitted. Urine: Start test in AM. Instruct patient to void completely. Discard this sample. Collect urine for five hours after administration of d-xylose.
Refrigerate plasma. Maintain urine specimen at room temperature. Urine sample is stable for 14 days at room temperature, refrigerated, or frozen. It is stable for two freeze/thaw cycles.
Plasma specimens not kept chilled; patient vomits test meal; loss of part of urine specimen and/or contaminated with stool