Test Overview

Test Methodology


Test Usage

Evaluate mucosal absorption efficiency in a variety of malabsorptive diseases. May be used for diagnosing cause of malabsorption.

Reference Range*

Age and dose specific reference ranges provided with report.

* Reference ranges may change over time. Please refer to the original patient report when evaluating results.

Test Limitations

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.

Test Details

Days Test Performed

Tuesday, Thursday

Analytic Time

3 - 10 days

Soft Order Code




d-Xylose Absorption Test
Xylose Tolerance Test

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Laboratory Reference

Mayo FXAB (91713) (ARUP 0020609 Adult 25 g dose), Mayo 91712 (ARUP 0020615 Adult 5 g dose), or Mayo FXAT (91711) (ARUP 0020612 Child)

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Specimen Requirements

Offsite Collection Instructions

MLabs does not provide d-xylose; client or physician will need to obtain d-xylose from a local pharmacy. 1) Patient should fast for 8 hours (minimum 4 hours) prior to administration of d-xylose. 2) Prior to administration of d-xylose, have patient empty bladder and discard urine. Collect a blood specimen in a red top tube from the fasting patient. 3) Dissolve 25 grams of d-xylose in 250 mL of water and administer, and follow immediately with an additional 250 mL of water. For patients who do not tolerate the 25 g dose, a 5 g dose can be used. For children aged

Special Handing

Fasting specimen.

Normal Volume

0.5 mL serum (pre- and post-dose) and 5 mL aliquot of 5 hour urine collection

Minimum Volume

0.5 mL serum (pre- and post-dose) and 3 mL aliquot of 5 hour urine collection

Additional Information

Test sent to Mayo Medical Laboratories; performed by ARUP Laboratories.

Billing Information

Fee Codes

CPT Code



3134-4 Blood, 3135-1 Urine

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