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Xylose Tolerance Test (Fasting + Two-hour Blood + Five-hour Urine−Adult)
- d-Xylose Tolerance Test
Fasting plasma xylose, two-hour (adult) postdose plasma xylose, plus five-hour urine xylose
Evaluate possible enterogenous malabsorption syndromes; test for functional integrity of the jejunum
This test was developed, and its performance characteristics determined, by LabCorp. It has not been cleared or approved by the Food and Drug Administration.
• Plasma: 2 hours: 32-58 mg/dL
• Urine: Adults 65 years or younger: >4.0 g/5 hours; adults older than 65 years: >3.5 g/5 hours
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's 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.
Plasma and urine
2 mL plasma (each specimen) and 10 mL aliquot of five-hour urine
0.6 mL plasma (each specimen) and 0.5 mL aliquot of five-hour urine
Adults: Plasma: Draw fasting and two-hour postdose blood samples (see Patient Preparation). Centrifuge and separate plasma. Indicate time drawn (ie, "fasting", "two-hour") on tubes. Urine: Collect entire five-hour urine volume. Send aliquot.
Causes for Rejection
Plasma specimen not kept chilled; patient vomits test meal; loss of part of urine specimen and/or contaminated with stool
Record five-hour urine total volume on the request form.
|Order Code||Order Code Name||Order Loinc||Result Code||Result Code Name||UofM||Result LOINC|
|293837||Xylose Tol 2-Hr/Adult/Urine||003510||Xylose, Urine, g/L||g/L||3135-1|
|293837||Xylose Tol 2-Hr/Adult/Urine||003511||Xylose, Urine, g/5hr||g/5 hr||1646-9|
|293837||Xylose Tol 2-Hr/Adult/Urine||016238||Xylose - Fasting||mg/dL||10872-0|
|293837||Xylose Tol 2-Hr/Adult/Urine||016634||Xylose - 2 hour||mg/dL||23943-4|
|293837||Xylose Tol 2-Hr/Adult/Urine||123101||Disclaimer:||N/A|