The xylose test is a medical procedure that assesses the ability of the small intestine to absorb nutrients. It is particularly useful for diagnosing malabsorption syndromes where the body does not absorb nutrients properly, such as coeliac disease or Crohn’s disease. In Germany, the test is carried out in clinical laboratories, with the urine method being the most common.

Implementation and significance

In the xylose test, the patient drinks 25 grams of D-xylose, a sugar that is passively absorbed through the small intestine, after a night of fasting. In the urine method, which is preferred in Germany, the patient collects their urine over 5 hours and the laboratory measures how much xylose has been excreted. Normally there should be 4.5-8 grams of xylose in the urine during this time. If less than 4 grams are excreted, this indicates impaired absorption, which can indicate diseases such as coeliac disease, tropical sprue or intestinal diseases.

The test is important to clarify the cause of symptoms such as weight loss, diarrhea or fatty stools. However, it has limitations: In patients with kidney disease, the urine method can be unreliable as the kidneys may not filter the xylose properly. In such cases, a blood test measuring the xylose concentration in the serum after 1-2 hours may be more helpful, with normal values above 20-30 mg/dL.

Special features in Germany

In Germany, laboratories follow the quality guidelines of the German Medical Association (RiliBÄK) to ensure the accuracy of the test. The test is available in many clinical laboratories, but it seems that it is used less frequently as more modern tests such as breath tests are available for specific conditions. Nevertheless, it remains useful when the cause of malabsorption is unclear. Patients must fast before the test and possibly discontinue certain medications that could affect intestinal mucosal function. The test is safe, with minimal side effects such as mild nausea or diarrhea.

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