d-Xylose Tolerance Test

d-Xylose Tolerance Test

Synonym/acronym: N/A.

Common use

To assist in the differential diagnosis of small intestine malabsorption syndromes such as celiac, tropical sprue, and Crohn’s diseases.

Specimen

Plasma (1 mL) collected in a gray-top (fluoride/oxalate) tube and urine (10 mL from a 5-hr collection) in a clean amber plastic container.

Normal findings

(Method: Spectrophotometry)
Dose GivenConventional UnitsSI Units (Conventional Units × 0.0666)
Plasma
Infant dose 0.5 g/kg (max. 25 g)Greater than 15 mg/dL after 2 hrGreater than 1 mmol/L
Pediatric dose 0.5 g/kg (max. 25 g)Greater than 20 mg/dL after 2 hrGreater than 1.3 mmol/L
Adult dose
25 gGreater than 25 mg/dL after 2 hrGreater than 1.7 mmol/L
5 g (given if patient is known or expected to have severe symptoms)Greater than 20 mg/dL after 2 hrGreater than 1.3 mmol/L
Urine
ChildrenGreater than 16%–40% of dose in 5 hr urine sample
AdultsGreater than 16% or greater than 4 g of dose in 5 hr urine sample
Older adults (age 65 years and older)Greater than 14% or greater than 3.5 g of dose in 5 hr urine sample

Description

The d-xylose tolerance test is used to screen for intestinal malabsorption of carbohydrates. d-Xylose is a pentose sugar not normally present in the blood in significant amounts. It is partially absorbed when ingested and normally passes unmetabolized in the urine.

This procedure is contraindicated for

    N/A

Indications

  • Assist in the diagnosis of malabsorption syndromes

Potential diagnosis

Increased in

    N/A

Decreased in

    Conditions that involve defective mucosal absorption of carbohydrates and other nutrients.

    Amyloidosis Bacterial overgrowth (sugar is consumed by bacteria) Eosinophilic gastroenteritis Lymphoma Nontropical sprue (celiac disease, gluten-induced enteropathy) Parasitic infestations (Giardia, schistosomiasis, hookworm) Postoperative period after massive resection of the intestine Radiation enteritis Scleroderma Small bowel ischemia Tropical sprue Whipple’s disease Zollinger-Ellison syndrome

Critical findings

    N/A

Interfering factors

  • Drugs that may increase urine d-xylose levels include phenazopyridine.
  • Drugs and substances that may decrease urine d-xylose levels include acetylsalicylic acid, aminosalicylic acid, arsenicals, colchicine, digitalis, ethionamide, gold, indomethacin, isocarboxazid, kanamycin, monoamine oxidase inhibitors, neomycin, and phenelzine.
  • Poor renal function or vomiting may cause low urine values.

Nursing Implications and Procedure

Pretest

  • Positively identify the patient using at least two unique identifiers before providing care, treatment, or services.
  • Patient Teaching:   Inform the patient this test can assist in assessing the ability of the small intestine to absorb carbohydrates.
  • Obtain a history of the patient’s complaints, including a list of known allergens, especially allergies or sensitivities to latex.
  • Obtain a history of the patient’s gastrointestinal system, symptoms, and results of previously performed laboratory tests and diagnostic and surgical procedures.
  • Obtain a list of the patient’s current medications, including herbs, nutritional supplements, and nutraceuticals (see Effects of Natural Products on Laboratory Values).
  • Review the procedure with the patient. Inform the patient that activity will be restricted during the test and that 1 or 2 blood specimens may be collected during the test. Obtain the pediatric patient’s weight to calculate dose of d-xylose to be administered. Inform the patient that blood specimen collection takes approximately 5 to 10 min. Address concerns about pain and explain that there may be some discomfort during the venipuncture.
  • Sensitivity to social and cultural issues,   as well as concern for modesty, is important in providing psychological support before, during, and after the procedure.
  • Ask the patient to void and discard the urine before the administration of the d-xylose. Inform the patient that once the test has begun, all urine for a 5-hr period must be saved. Provide a nonmetallic urinal, bedpan, or toilet-mounted collection device.
  • Instruct the patient not to void directly into the laboratory collection container. Instruct the patient to avoid defecating in the collection device and to keep toilet tissue out of the collection device to prevent contamination of the specimen. Place a sign in the bathroom to remind the patient to save all urine.
  • Instruct the patient to void all urine into the collection device and then to pour the urine into the laboratory collection container. Alternatively, the specimen can be left in the collection device for a health-care staff member to add to the laboratory collection container.
  • Numerous medications (e.g., acetylsalicylic acid, indomethacin, neomycin) interfere with the test and should be withheld, by medical direction, for 24 hr before testing.
  • Note that there are no fluid restrictions, unless by medical direction.
  • Instruct the patient to fast for at least 12 hr before the test. In addition, the patient should refrain from eating foods containing pentose sugars such as fruits, jams, jellies, and pastries. Protocols may vary among facilities.

Intratest

  • Potential complications: N/A
  • Ensure that the patient has complied with dietary and medication restrictions; assure that food has been restricted for at least 12 hr prior to the procedure and medications have been withheld, by medical direction, for 24 hr prior to the procedure.
  • Avoid the use of equipment containing latex if the patient has a history of allergic reaction to latex.
  • Instruct the patient to cooperate fully and to follow directions. Direct the patient to breathe normally and to avoid unnecessary movement.
  • Observe standard precautions, and follow the general guidelines in Patient Preparation and Specimen Collection. Positively identify the patient, and label the appropriate specimen container with the corresponding patient demographics, initials of the person collecting the specimen, date, and time of collection. Perform a venipuncture to collect a pre-dose specimen.
  • Remove the needle and apply direct pressure with dry gauze to stop bleeding. Observe/assess venipuncture site for bleeding or hematoma formation and secure gauze with adhesive bandage.
  • Timed Specimen

  • Obtain a clean 3-L urine specimen container, toilet-mounted collection device, and plastic bag (for transport of the specimen container). The specimen must be refrigerated or kept on ice throughout the entire collection period. If an indwelling urinary catheter is in place, the drainage bag must be kept on ice.
  • Begin the test between 6 a.m. and 8 a.m., if possible. Remind the patient to remain supine and at rest throughout the duration of the test. Instruct the patient to collect all urine for a 5-hr period after administration of the d-xylose.
  • Adults are given a 25-g dose of d-xylose dissolved in 250 mL of water to take orally. The dose for pediatric patients is calculated by weight up to a maximum of 25 g. The patient should drink an additional 250 mL of water as soon as the d-xylose solution has been taken. Some adult patients with severe symptoms may be given a 5-g dose, but the test results are less sensitive at the lower dose.
  • If an indwelling catheter is in place, replace the tubing and container system at the start of the collection time. Keep the container system on ice during the collection period or empty the urine into a larger container periodically during the collection period; monitor to ensure continued drainage.
  • Blood samples are collected 1 hr postdose for pediatric patients and 2 hr postdose for adults.
  • Direct the patient to breathe normally and to avoid unnecessary movement. Perform a venipuncture, and collect the specimen in a 5-mL gray-top tube.
  • Include on the collection container’s label the amount of urine, test start and stop times, and ingestion of any foods or medications that could affect test results.
  • Promptly transport the specimens to the laboratory for processing and analysis.

Post-Test

  • Inform the patient that a report of the results will be made available to the requesting health-care provider (HCP), who will discuss the results with the patient.
  • Instruct the patient to resume usual medications, as directed by the HCP.
  • Nutritional Considerations: Decreased d-xylose levels may be associated with gastrointestinal disease. Nutritional therapy may be indicated in the presence of malabsorption disorders. Encourage the patient, as appropriate, to consult with a qualified nutrition specialist to plan a lactose- and gluten-free diet. This dietary planning is complex because patients are often malnourished and have related nutritional problems.
  • Recognize anxiety related to test results. Discuss the implications of abnormal test results on the patient’s lifestyle. Provide teaching and information regarding the clinical implications of the test results, as appropriate. Offer support to help the patient and/or caregiver cope with the long-term implications of a chronic disorder and related lifestyle changes. Educate the patient regarding access to counseling services, as appropriate.
  • Reinforce information given by the patient’s HCP regarding further testing, treatment, or referral to another HCP. Answer any questions or address any concerns voiced by the patient or family.
  • Depending on the results of this procedure, additional testing may be performed to evaluate or monitor progression of the disease process and determine the need for a change in therapy. Evaluate test results in relation to the patient’s symptoms and other tests performed.

Related Monographs

  • Related tests include biopsy intestine, chloride sweat, fecal analysis, fecal fat, gastric emptying scan, lactose tolerance, ova and parasite, and RAIU.
  • Refer to the Gastrointestinal System table at the end of the book for related tests by body system.