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Home > Health Library > 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:
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 doctor 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.
A D-xylose test can take a long time. It might be a good idea to bring something you can do quietly while you wait, such as a book to read.
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 are 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.
The health professional taking a sample of your blood will:
You will not be allowed to eat until the test is completed.
Drinking the D-xylose solution can make you feel sick to your stomach (nauseated).
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.
There is no pain while collecting a 5-hour urine sample.
There is very little chance of a problem from having a blood sample taken from a vein.
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 vomiting and 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 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 can't 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 doctor will discuss any significant abnormal results with you in relation to your symptoms and past health.
The normal values listed here—called a reference range—are just a guide. These ranges vary from lab to lab, and your lab may have a different range for what's normal. Your lab report should contain the range your lab uses. Also, your doctor will evaluate your results based on your health and other factors. This means that a value that falls outside the normal values listed here may still be normal for you or your lab.
Infants (5-gram dose):
More than 15 milligrams per deciliter (mg/dL) or more than 1.0 millimole per liter (mmol/L)
Children (5-gram dose):
More than 20 mg/dL or more than 1.3 mmol/L
Adults (5-gram dose):
More than 20 mg/dL in 2 hours or more than 1.3 mmol/L
Adults (25-gram dose):
More than 25 mg/dL in 2 hours or more than 1.6 mmol/L
16%–33% of the D-xylose dose is found in the sample.
More than 16% of the D-xylose doseor more than 4 grams (g) is found in the sample.
Adults age 65 and older:
More than 14% of the D-xylose doseor more than 3.5 g is found in the sample.
Low values may be caused by:
Reasons you may not be able to have the test or why the results may not be helpful include:
Current as of
Author: Healthwise StaffMedical ReviewE. Gregory Thompson MD - Internal MedicineAdam Husney MD - Family MedicineMartin J. Gabica MD - Family Medicine
Fischbach FT, Dunning MB III, eds. (2009). Manual of Laboratory and Diagnostic Tests, 8th ed. Philadelphia: Lippincott Williams and Wilkins.
Current as of:
March 28, 2019
Medical Review:E. Gregory Thompson MD - Internal Medicine & Adam Husney MD - Family Medicine & Martin J. Gabica MD - Family Medicine
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