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
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
Why It Is Done
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
How To Prepare
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
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.
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?).
How It Is Done
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:
- 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
- Put the needle into the vein. More than one needle stick
may be needed.
- Attach a tube to the needle to fill it with
- Remove the band from your arm when enough blood is
- 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
- 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
- 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