Xylose Tolerance Test (Fasting + One-hour Blood Without Five-hour Urine-Pediatric)

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Turnaround Time: 3 - 4 days
CPT Code:


Test Type: 0.6 mL (each specimen) Plasma
Reference Range:

Xylose − Fasting mg/dL N/A
Xylose − 1 hour mg/dL 21 − 57
Child: >30


Evaluate possible enterogenous malabsorption syndromes; testfor functional integrity of the jejunum Xylose is a pentose found naturally occurring in certain fruits such as plums. It is not normally found in significant concentrations in blood or urine thereby rendering the duodenojejunal absorption of d-xylose a useful mechanism to assess the integrity of the gastrointestinal mucosa. D-xylose is passively absorbed by the small bowel with some 30% to 40% of the ingested dose rapidly excreted in the urine. Absorption into the blood is evaluated at specific time intervals with intestinal malabsorption being indicated by low absorption values. Low values would likewise be seen in celiac diseases, tropical sprue, Crohn disease, immunoglobulin deficiency, pellagra, ascariasis, blind loop syndrome, radiation enteritis, surgical bowel resection, vomiting, delayed gastric emptying, inadequate hydration, decreased circulation, intrinsic renal disease, thyroid disease, ascites, and increased intestinal motility from any cause. The d-xylose absorption test may be of some help in distinguishing pancreatic insufficiency from jejunal malabsorption. Essentially normal d-xylose absorption values will be obtained in malabsorption values due to pancreatic insufficiency, whereas low blood values will be obtained in jejunal malabsorption. Urine values for xylose excretion are useful in determining renal insufficiency. Diminished excretion of d-xylose could be indicative of renal insufficiency, thereby invalidating the blood xylose absorption results. Low urine xylose values could also be attributed to incomplete collection or urinary retention.

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

Collection Details:

Patient Preparation:

Pediatric patients (younger than nine years) must be fastingfor at least four hours prior to administration of d-xylose (LabCorp ID 26599, containing 25 g d-xylose). Patient must remain in supine position for duration of test. No food is permitted during the test. Patient should refrain from eating foods containing pentose and medication especially aspirin, neomycin, colchicine, indomethacin, or atropine) for 24 hours prior to the test. These include fruits, jams, jellies and pastries containing these items. No water restriction; in fact, patient should be encouraged to drink during the fasting period and during the test. Start test inAM. Draw fasting blood specimen. 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. Have patient drink entire amount. Fill cup with 250 mL water and have patient drink this also. Have patient drink another cup with 250 mL water after one hour. Draw remaining blood specimens. (children: one hour)

Collection Instructions:

Gray-top (sodium fluoride) tube and plastic urine container.

Pediatric: PLASMA: Draw fasting and one-hour postdose blood samples (See Patient Preparation). Centrifuge and separate plasma from cells immediately. Indicate time drawn (ie, "fasting", "one-hour") on each plasma tube.