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Xylose Tolerance Test (Fasting + Two-hour Blood + Five-hour Urine−Adult)/ Xylose Tolerance Test (Fasting + Two-hour Blood + Five-hour Urine−Adult)

Test ID: 

703162/ 703165

CPT code:



d-Xylose Tolerance Test

Clinical Use:

Evaluate possible enterogenous malabsorption syndromes; test for functional integrity of the jejunum

Specimen Type:

Plasma and urine/ Plasma

Requested Volume: 

2 mL plasma (each specimen) and 10 mL aliquot of five-hour urine/ 2 mL (each specimen)

Minimum Volume: 

1 mL (each specimen)/ 1 mL (each specimen)

Container Type: 

Gray-top (sodium fluoride) tube and plastic urine container

Patient Preparation: 

Patient must fast a minimum of eight hours prior to administration of d-xylose. 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 medication especially aspirin, neomycin, colchicine, indomethacin, or atropine for 24 hours prior to the test. These include fruits, jams, jellies and pastries containing these items. 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 (adults: two hours).


Adults: Plasma: Draw fasting and two-hour postdose blood samples (see Patient Preparation). Centrifuge and separate plasma. Indicate time drawn (ie, “fasting”, “two-hour”) on tubes. Urine: Collect entire five-hour urine volume. Send aliquot.

Storage Instructions:

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.

Rejection Criteria

Plasma specimen not kept chilled; patient vomits test meal; loss of part of urine specimen and/or contaminated with stool

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