Xylose Tolerance Test (Fasting, One-, Two-, Three-, Four-, and Five-hour Blood + Five-hour Urine)

CPT: 84620
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Test Details


  • d-Xylose Tolerance

Test Includes

Specimens drawn fasting, one, two, three, four, and five hours plus five-hour urine xylose result


Diagnose intestinal malabsorption syndromes


This test was developed, and its performance characteristics determined, by LabCorp. It has not been cleared or approved by the Food and Drug Administration.



Reference Interval

• Plasma:

− Children: 1 hour: >30 mg/dL

− Adults: 1 hour: 21−57 mg/dL, 2 hours: 32−58 mg/dL, 3 hours: 19−42 mg/dL, 4 hours: 11−29 mg/dL, 5 hours: 6−18 mg/dL

• Urine:

− Children: 16% to 33% of ingested dose

− Adults: 65 years or younger: >4.0 g/5 hours; older than 65 years: >3.5 g/5 hours

Specimen Requirements


Plasma and urine


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

Minimum Volume

0.6 mL plasma (each specimen) and 0.5 mL aliquot of five-hour urine


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 (LabCorp N° 26599, containing 25 g 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.

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.

Causes for Rejection

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

Clinical Information

Special Instructions

Record total five-hour urine volume on the test request form.


May cause mild diarrhea


Order Code Order Code Name Order Loinc Result Code Result Code Name UofM Result LOINC
023374 Xylose Tolerance 5-Hr/Urine 016238 Xylose - Fasting mg/dL 10872-0
023374 Xylose Tolerance 5-Hr/Urine 016626 Xylose - 1 hour mg/dL 23940-0
023374 Xylose Tolerance 5-Hr/Urine 016634 Xylose - 2 hour mg/dL 23943-4
023374 Xylose Tolerance 5-Hr/Urine 016246 Xylose - 3 hour mg/dL 10869-6
023374 Xylose Tolerance 5-Hr/Urine 016329 Xylose - 4 hour mg/dL 13030-2
023374 Xylose Tolerance 5-Hr/Urine 016337 Xylose - 5 hour mg/dL 13031-0
023374 Xylose Tolerance 5-Hr/Urine 003510 Xylose, Urine, g/L g/L 3135-1
023374 Xylose Tolerance 5-Hr/Urine 003511 Xylose, Urine, g/5hr g/5 hr 1646-9
023374 Xylose Tolerance 5-Hr/Urine 123101 Disclaimer: N/A

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