Xylose Tolerance Test (Fasting + One-hour Blood + Five-hour Urine−Pediatric)/ Xylose Tolerance Test (Fasting + One-hour Blood Without Five-hour Urine−Pediatric)
d-Xylose Tolerance Test
Evaluate possible enterogenous malabsorption syndromes; test for functional integrity of the jejunum
Xylose is a pentose found naturally occurring in certain fruits such as plums. It is not normally found in significant concentrations in blood or urine thereby rendering the duodenojejunal absorption of d-xylose a useful mechanism to assess the integrity of the gastrointestinal mucosa.
Plasma and urine/ Plasma
2 mL plasma (each specimen) and 10 mL aliquot of five-hour urine/ 0.6 mL (each specimen)
0.6 mL plasma (each specimen) and 0.5 mL aliquot of five-hour urine/ 0.6 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) must be fasting for at least four hours. Patient must remain in supine position for duration of test except during urine collection. No food is permitted during the test. Patient should refrain from eating foods containing pentose and medications (especially aspirin, neomycin, colchicine, indomethacin, or atropine) for 24 hours prior to the test. Foods containing pentose include fruits, jams, jellies, and pastries. No water restriction; in fact, patient should be encouraged to drink during the fasting period and during test. Start test in the AM. Instruct patient to void completely. Discard this urine. Draw fasting blood specimen. 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. Have patient drink entire amount. Fill cup with 250 mL water and have patient drink this also. Have patient drink another cup with 250 mL water after one hour. Collect urine for five hours after administration of d-xylose. Record total five-hour urine volume and send aliquot. Record total on the request form. Draw remaining blood specimens (children: one hour).
Record five-hour urine total volume on the request form.
Plasma: Draw fasting and one-hour postdose blood samples (See Patient Preparation). Centrifuge and separate plasma from cells immediately. Indicate time drawn (ie, “fasting”, “one-hour”) on each plasma tube.
Urine: Collect entire five-hour urine volume. Send aliquot.
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 specimen not kept chilled; patient vomits test meal; loss of part of urine specimen and/or contaminated with stool