D-xylose absorption test. Urine or blood?

Area of Science:

• Gastroenterology
• Diagnostic Testing
• Clinical Medicine

Background:

• The D-xylose absorption test is a long-standing method for diagnosing small intestine malabsorption.
• Debate exists regarding the optimal protocol: 1-hour blood test, 5-hour urine test, or combined approach.

Purpose of the Study:

• To evaluate and compare the diagnostic accuracy of the 1-hour blood D-xylose test versus the 5-hour urine D-xylose test.
• To determine the most reliable method for assessing intestinal absorption.

Main Methods:

• A combined 1-hour blood and 5-hour urine D-xylose absorption test was performed on 111 patients.
• Results were categorized based on normal or abnormal values for both blood and urine tests.
• Further investigations including stool fat analysis and [14C]cholylglycine breath test were used to confirm malabsorption in specific patient groups.

Main Results:

• Normal xylose absorption was observed in both blood and urine tests in 56.8% of patients.
• Abnormal results in both tests occurred in 23.2% of patients.
• A significant proportion (19.2%) showed normal blood xylose but abnormal urine xylose, with confirmed fat/bile salt malabsorption in 87.5% of this subgroup.

Conclusions:

• The 5-hour urine D-xylose test appears to be a more accurate reflection of intestinal absorption in adults compared to the 1-hour blood test.
• Discrepancies between blood and urine tests highlight the importance of considering the urine test for comprehensive malabsorption evaluation.