ARUP's Laboratory Test Directory

0020615: Xylose Absorption Test (Adult - 5g dose)

Test Mnemonic: XYL-5G
Methodology: Spectrophotometry

Performed: Tue, Thu

Reported: 1-5 days

Specimen Required:  
Collect: •The patient should fast for eight hours (minimum four hours) prior to starting test.
• Just prior to start of test, the patient should empty his or her bladder (DO NOT collect this urine).
• Just prior to start of test, collect the first serum sample.  (Min: 0.5 mL serum) Label this sample as "FASTING SERUM."
• 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.
• Collect the second serum sample two hours after giving the xylose dose.  (Min: 0.5 mL serum) Label this sample as "TWO-HOUR SERUM."
• After giving 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) for transport. Label this sample as "FIVE-HOUR URINE."

Record the xylose dose given and the total volume of the five-hour urine on the test request form. 
Send and label the fasting and two-hour serum samples. 
Record the total volume and the xylose dose given on the urine aliquot tube.
Failure to include required information will result in delay of turnaround time.

Transport: One "FASTING SERUM," one "TWO-HOUR SERUM," and one "FIVE-HOUR URINE" aliquot at 2-8°C. Please label samples completely.  Record total five-hour urine volume on urine aliquot tube and dose of xylose given on test request form.

Pediatric Collection/Transport: Refer to Xylose Absorption Test (Child) (0020612).

Remarks: Serum is the preferred blood sample. Allow serum to clot completely at room temperature.  Separate serum from cells ASAP. The "fasting" serum sample does not have a reference interval since it is used as a blank for the two-hour serum sample.

Unacceptable Conditions: Grossly hemolyzed serum and nonfasting samples. Whole blood or unspun clot tubes.

Stability: Ambient: 4 hours; Refrigerated: 1 week; Frozen: 1 month

Reference Interval:
 
Components Reference Interval
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

Note:
The xylose absorption test evaluates carbohydrate absorption by the mucosa of the proximal small intestine. In patients with renal deficiency, rely on the serum test only. In functionally anephric patients, the test is unreliable. A number of drugs can interfere with test results, including: aspirin, atropine, colchicine, digitalis, indomethacin, MAO inhibitors, nalidixic acid, neomycin, opium alkaloids, and phenelzine. Nonfasting serum samples are often compromised by significant analytic interferences.

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.

CPT Code(s):
84620