Nonstandard test for determining cause of malabsorption. Test evaluates carbohydrate absorption of the proximal small intestine.
- Patient Preparation
- Children are defined as less than 17 years old for purposes of this test. Patient should fast for 8 hours (Min: 4 hours) prior to administration of xylose.
- Fasting serum, five-hour urine, and one-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 children 0.5 g D-xylose per kilogram of body weight, up to 25 g; give xylose in water (5 mL of water per 0.5 g of xylose, up to 250 mL water). Encourage the patient to drink additional water following the xylose dose. The patient may have water as desired, but no other food or fluids. 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. One hour 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 "ONE-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.
-If unable to collect pediatric urine samples, testing will be completed with a disclaimer, provided both serum specimens are received.
-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.
- Ambient: 4 hours; Refrigerated: 1 week; Frozen: 1 month
|Serum, fasting specimen|
(There are no reference intervals for the fasting specimen; it is used as a patient "blank" when testing the one-hour specimen.)
|0-16 years: None|
|Serum xylose, one hour following ingestion||0-5 months: 15-58 mg/dL|
6 months-16 years: 20-58 mg/dL
|Fraction of xylose dose excreted in five hours in urine||0-16 years: 16-40% of dose|
|Amount of xylose excreted in five hours in urine||0-16 years: depends on dose given|
|Component Test Code*||Component Chart Name||LOINC|
|0020085||Serum Xylose 60 Minutes||10453-9|
|0020088||Xylose Excretion % Dose 5 hr||22630-8|
|0020600||Xylose Excretion, g/5hr||22626-6|
- Xylose Child
- Xylose Tolerance Test