D-xylose Absorption Test

The D-xylose absorption test measures the level of D-xylose, a type of sugar, in a blood or urine sample. This test is done to help diagnose problems that prevent the small intestine from absorbing nutrients in food.

D-xylose is normally easily absorbed by the intestines. When problems with absorption occur, D-xylose is not absorbed by the intestines, and its level in blood and urine is low.

A test for D-xylose is done to:

• Check to see if malabsorption syndrome is causing symptoms, such as chronic diarrhea, weight loss, and weakness. A person with malabsorption syndrome is unable to absorb nutrients, vitamins, and minerals from the intestinal tract into the bloodstream.
• Find the cause of a child's failure to gain weight, especially when the child seems to be eating enough food.

For 24 hours before a D-xylose test, do not eat foods high in pentose, a sugar similar to D-xylose; these foods include fruits, jams, jellies, and pastries.

Medicines such as aspirin and indomethacin can interfere with the results of a D-xylose test. For this reason, your health professional may instruct you to temporarily stop these medicines before the test.

Do not eat or drink anything except water for 8 to 12 hours before having this test. Children younger than 9 years old should not eat or drink anything except water for 4 hours before the test.

Talk to your doctor about any concerns you have regarding the need for the test, its risks, how it will be done, or what the results will mean. To help you understand the importance of this test, fill out the medical test information form(What is a PDF document?).

The amount of D-xylose in urine and blood samples is measured before and after you drink a D-xylose solution. To begin the test, a sample of your first urine of the day and a sample of your blood is collected.

Next you will drink a D-xylose solution. For adults, a blood sample is usually taken 2 hours after drinking the solution. For children, a blood sample may be taken 1 hour after drinking the solution. Another blood sample may be drawn 5 hours after drinking the solution.

You will need to collect all of the urine you produce for 5 hours after drinking the sugar solution. Sometimes urine is collected for 24 hours after drinking the sugar solution.

Blood test

The health professional taking a sample of your blood will:

• Wrap an elastic band around your upper arm to stop the flow of blood. This makes the veins below the band larger so it is easier to put a needle into the vein.
• Clean the needle site with alcohol.
• Put the needle into the vein. More than one needle stick may be needed.
• Attach a tube to the needle to fill it with blood.
• Remove the band from your arm when enough blood is collected.
• Put a gauze pad or cotton ball over the needle site as the needle is removed.
• Put pressure to the site and then put on a bandage.

Urine test

• You start collecting your urine in the morning. When you first get up, empty your bladder but do not save this urine. Write down the time that you urinated to mark the beginning of your 5-hour collection period.
• For the next 5 hours, collect all your urine. Your doctor or lab will usually provide you with a large container that holds about 1 gal (4 L). The container has a small amount of preservative in it. Urinate into a small, clean container and then pour the urine into the large container. Do not touch the inside of the container with your fingers.
• Keep the large container in the refrigerator during the collection period.
• Empty your bladder for the final time at or just before the end of the 5-hour period. Add this urine to the large container and record the time.
• Do not get toilet paper, pubic hair, stool (feces), menstrual blood, or other foreign matter in the urine sample.

You will not be allowed to eat until the test is completed.

Blood test

The blood sample is taken from a vein in your arm. An elastic band is wrapped around your upper arm. It may feel tight. You may feel nothing at all from the needle, or you may feel a quick sting or pinch.

Urine test

There is no pain while collecting a 5-hour urine sample.

Blood test

There is very little chance of a problem from having a blood sample taken from a vein.

• You may get a small bruise at the site. You can lower the risk of bruising by keeping pressure on the site for several minutes.
• In rare cases, the vein may become swollen after the blood sample is taken. This problem is called phlebitis. A warm compress can be used several times a day to treat this.
• Ongoing bleeding can be a problem for people with bleeding disorders. Aspirin, warfarin (Coumadin), and other blood-thinning medicines can make bleeding more likely. If you have bleeding or clotting problems, or if you take blood-thinning medicine, tell your doctor before your blood sample is taken.

Urine test

This test can cause dehydration. Make sure that you drink enough fluids to replace lost liquids after you have completed the test.

Drinking the D-xylose preparation may cause nausea, vomiting, or diarrhea. Tell your doctor if you have problems after drinking the D-xylose solution.

The D-xylose test measures the level of D-xylose, a type of sugar, in a blood or urine sample.

Blood levels of D-xylose are highest about 2 hours after the drinking the D-xylose solution. Almost all of the D-xylose is eliminated from the body in the urine within 5 hours. If the intestines cannot absorb the D-xylose properly, the amount of D-xylose in the blood and urine will be very low.

Many conditions can change D-xylose levels. Your health professional will discuss any significant abnormal results with you in relation to your symptoms and past health.

Normal

Normal values may vary from lab to lab.

High values

High values may be caused by:

• A disease, such as Hodgkin's disease or scleroderma.
• Radiation treatment.

Low values

Low values may be caused by:

• A disease that interferes with the intestine's ability to absorb nutrients (malabsorption syndrome), such as Crohn's disease, celiac disease, or Whipple's disease.
• Inflammation of the lining of the intestine.
• An infection with a parasite, such as giardiasis or hookworm.

Factors that can interfere with your test or the accuracy of the results include:

• Large amounts of bacteria in the intestines.
• Kidney disease or bladder problems that prevent you from completely emptying your bladder.
• Medicines, such as antibiotics, aspirin, and heart medicines. Many medicines can affect D-xylose test results.
• Physical activity during the test. You will be instructed to rest quietly until the test is complete.
• Conditions that cause food to remain in the stomach for a long time.

• If you have an abnormally high amount of bacteria in your intestines, you may have to take antibiotics for a day or two before the test.
• This test can cause dehydration. Make sure that you drink enough fluids to replace lost liquids after you have completed the test. Tell your health professional if you have problems with diarrhea after drinking the D-xylose solution.
• Blood D-xylose levels are generally considered more reliable than urine levels in children younger than 12 years old.
• A test that looks at the lining of the small intestines (upper gastrointestinal series) may be used if Crohn's disease or another malabsorption syndrome is suspected. For more information, see the medical test Upper Gastrointestinal Series.

Other Works Consulted

• Chernecky CC, Berger BJ, eds. (2004). Laboratory Tests and Diagnostic Procedures, 4th ed. Philadelphia: Saunders.

• Fischbach FT, Dunning MB III, eds. (2004). Manual of Laboratory and Diagnostic Tests, 7th ed. Philadelphia: Lippincott Williams and Wilkins.

• Pagana KD, Pagana TJ (2006). Mosby’s Manual of Diagnostic and Laboratory Tests, 3rd ed. St. Louis: Mosby.