What Is a D-Xylose
A D-xylose absorption test is used to
check how well your intestines are absorbing a simple sugar called D-xylose.
From the results of the test, your doctor can infer how well your body is absorbing
D-xylose is a simple sugar that occurs
naturally in many plant foods. Your intestines usually absorb it easily, along
with other nutrients. To see how well your body is absorbing D-xylose, your
doctor will usually first use blood and urine tests. These tests will show low
D-xylose levels in your blood and urine if your body is not absorbing D-xylose well.
What the Test Addresses
The D-xylose absorption test is not commonly
done. However, one instance when your doctor may prescribe this
test is when earlier blood and urine tests show that your intestines are not
absorbing D-xylose properly. In this case, your doctor may want you to carry
out the D-xylose absorption test to determine if you have malabsorption
syndrome. This is caused when your small intestine, which is responsible for
most of your food digestion, can't absorb sufficient nutrients from your daily
diet. Malabsorption syndrome can cause symptoms such as weight loss, chronic
diarrhea, and extreme weakness and fatigue.
Preparation for the Test
You should not eat foods containing
pentose for 24 hours before a D-xylose absorption test. Pentose is a sugar that
is similar to D-xylose. Foods high in pentose include:
Your doctor may advise you to stop
taking medicines such as indomethacin
and aspirin prior to your test, as these can interfere with the results.
You should not eat or drink anything
except water for eight to 12 hours prior to the test. Children should avoid
eating and drinking anything but water for four hours prior to the test.
How Is the Test Done?
The test requires both a blood and urine
sample. Your doctor will ask you to drink 8 ounces of water containing 25 grams
of D-xylose sugar. Two hours later, they'll collect a blood sample. You’ll need
to give another blood sample after another three hours. After eight hours,
you’ll need to give a urine sample. The amount of urine you produce over a
five-hour period will also be measured.
The Blood Sample
Blood will be drawn from a vein in
your lower arm or the back of your hand. First your doctor or medical
technician will swab the site with antiseptic, and will then wrap an elastic
band around the top of your arm to cause the vein to swell with blood. Your
doctor or technician will then insert a fine needle into the vein and collect a
blood sample into a tube attached to the needle. The band is removed and gauze
is applied to the site to prevent any further bleeding.
The Urine Sample
You’ll begin collecting your urine the
morning on the day of the test. Don’t bother collecting the urine from when you
first get up and empty your bladder. Start collecting urine from the second
time you urinate. Make a note of the time of your second urination so your
doctor knows when you began your five-hour collection. Collect all your urine
over the next five hours. Your doctor will provide you with a large, sterile
container that usually holds about 1 gallon. It’s easiest if you urinate into a
small container and add the sample to the larger container. Be careful not to
touch the inside of the container with your fingers. Don’t get any pubic hair,
stool, menstrual blood, or toilet paper in the urine sample. These might
contaminate the sample and skew your results.
Understanding the Results
Your test results go to a laboratory
for analysis. If your tests show you have abnormally
low levels of D-xylose, it could mean you have one of following conditions:
- short bowel syndrome, a disorder that may occur
in people who have had at least one-third of their bowel removed
- infection by a parasite such as hookworm
- inflammation of the intestinal lining
- food poisoning or the flu
What Are the Risks of the Test?
As with any blood test, there’s
minimal risk of minor bruising at the needle site. In rare cases, the vein may
become swollen after blood is drawn. This condition, known as phlebitis, can be
treated with a warm compress several times each day. Ongoing bleeding could be
a problem if you suffer from a bleeding disorder or if you’re taking
blood-thinning medication such as warfarin
(Coumadin) or aspirin.
Following Up After a D-xylose
If your doctor suspects you have
malabsorption syndrome, they may recommend a test to examine the lining of your
If you have an intestinal parasite, your
doctor will do an additional test to see what the parasite is and how to treat
If your doctor believes you have short
bowel syndrome, they’ll recommend dietary changes or prescribe medication.
Depending on the results of your test,
your doctor will work with you to create an appropriate treatment plan.