Xylose Testing
A xylose test measures the levels of a specific sugar in your blood and urine to evaluate how well your intestines absorb nutrients.
Overview
Xylose, also known as D-xylose, is a type of sugar that is normally easily absorbed by your intestines. A xylose test checks the level of xylose in both your blood and urine to see how well your body absorbs carbohydrates. If you do not have enough bile or pancreatic enzymes, your body cannot digest food properly, which may result in lower-than-normal xylose levels indicating a potential problem with nutrient absorption.
Xylose testing is no longer routinely ordered and may not be available everywhere. It is sometimes used as a follow-up to other procedures, such as a fecal fat test.
What is it used for?
A xylose test is most often used to:
- Help diagnose malabsorption disorders, which affect your ability to digest and absorb nutrients.
- Determine why a child is not gaining weight despite adequate food intake.
Why do I need a xylose test?
Your provider may order this test if you exhibit symptoms of a malabsorption disorder, including:
- Chronic diarrhea
- Abdominal pain
- Bloating or a feeling of fullness
- Gas
- Unexplained weight loss or failure to gain weight in children
What happens during a xylose test?
The test involves taking timed samples of blood and urine before and after you drink a solution containing a small amount of xylose mixed with water.
Blood Tests
- A health care professional will collect a fasting blood sample from a vein in your arm.
- You will drink the xylose solution and rest quietly.
- A second blood sample will be taken two hours later (or one hour later for children).
Urine Tests
- You must empty your bladder before starting the test (this sample is not saved).
- After drinking the solution, you will collect all urine produced over the next five hours according to your provider's instructions.
Preparation and Risks
You must fast for eight hours before the test (four hours for children younger than nine). For 24 hours prior, avoid foods high in pentose, such as jams, pastries, and fruits. Consult your provider regarding any medications you are currently taking.
Risks are minimal. You may experience slight pain or bruising at the needle site, and the xylose solution may cause nausea. There is no risk associated with the urine collection.
What do the results mean?
High levels of xylose are considered normal, indicating that your intestines are absorbing the sugar correctly. Lower-than-normal levels may suggest a malabsorption disorder, such as:
- Celiac disease: A chronic digestive and immune disorder triggered by gluten.
- Crohn's disease: A condition causing inflammation in the digestive tract.
- Whipple disease: A rare condition preventing nutrient absorption.
- Parasitic infections: Such as hookworm or giardiasis.
If blood levels are normal but urine levels are low, it may indicate kidney disease or malabsorption. Your provider will interpret these results alongside your medical history and other diagnostic tests.