Nonstandard test for determining cause of malabsorption. Test evaluates carbohydrate absorption of the proximal small intestine. 5g dose is preferred in patients who do not tolerate the 25g dose.
- Patient Preparation
- Patient should fast for 8 hours (Min: 4 hours) prior to administration of xylose.
- Fasting serum, five-hour urine, and two-hour serum according to the following instructions.
- Specimen Preparation
- 1. Just prior xylose administration, patient should empty his or her bladder (DO NOT collect this urine).
2. Just prior to xylose administration, collect first serum specimen (Min: 0.5 mL). Allow serum to clot completely at room temperature. Separate serum from cells ASAP or within 2 hours of collection. Label this specimen as "FASTING SERUM" and prepare for transport.
3. Give adults 5 g D-xylose in 250 mL water. Encourage the patient to drink an additional 250 mL water following the xylose dose. The patient may have water as desired, but no other food or fluids. Smoking should be prohibited. The patient should rest in a chair or on a bed until completion of test. Mild diarrhea is common following xylose ingestion.
4. Immediately following the xylose dose, collect all urine for the next five hours. Measure and record the volume, mix well, and remove a 5 mL aliquot (Min: 3 mL) and prepare for transport. Label this specimen as "FIVE-HOUR URINE." Record the total volume and the xylose dose given on the urine aliquot tube.
5. Two hours after administration of xylose dose, collect the second serum specimen (Min: 0.5 mL). Allow serum to clot completely at room temperature. Separate serum from cells ASAP or within 2 hours of collection. Label this specimen as "TWO-HOUR SERUM" and prepare for transport.
6. Record the xylose dose given and the total volume of the five-hour urine on the test request form.
Failure to include all required information will result in delay of turnaround time.
- Storage/Transport Temperature
- Unacceptable Conditions
- Non-fasting specimens. Whole blood or unspun clot tubes. Grossly hemolyzed serum.
- The fasting serum specimen does not have a reference interval since it is used as a blank for the two-hour serum sample.
For children, refer to Xylose Absorption Test (Child) (ARUP test code 0020612).
- Ambient: 4 hours; Refrigerated: 1 week; Frozen: 1 month
|Serum, fasting specimen|
(There are no reference intervals for the fasting serum specimen; it is used as a patient "blank" when testing the two-hour specimen.)
|17 years and older: None|
|Serum xylose, two hours following ingestion||17 years and older: 5-17 mg/dL|
|Fraction of xylose dose excreted in five hours in urine||17 years and older: 20-40% of dose|
|Amount of xylose dose excreted in five hours in urine||17 years and older: 1.2-2.0 g/5 hours|
The xylose absorption test can be performed using a 25 g dose of xylose. Refer to Xylose Absortion Test (Adult-25 g dose) (0020609) or a 5 g dose, refer to Xylose Absortion Test (Adult -5 g) (0020615) as described here. The 5 g dose is generally preferred in patients who do not tolerate the 25 g dose.
|Component Test Code*||Component Chart Name||LOINC|
|0020616||Serum Xylose at 2 Hours||29913-1|
|0020617||Xylose Excretion, g/5 hrs||22627-4|
|0020618||Xylose Excretion, % Dose 5 hr||22631-6|
- Xylose Tolerance Test