Carbon-13 labeled D-xylose breath test

D-xylose is 5-carbon monosacharide (pentose). About 60% is passively absorbed in the proximal part of the small intestine (duodenojejunal) and is eliminated from the circulation by the kidneys. Clearance cca 87 % is due to the tubular resorption of D-xylose. In the classic stress test with D-xylose, 5-25 g of D-xylose is administred orally. In the laboratory is determined the level in serum and urine in the fasted state and 5 hours after the application of the load (a 5-hour urine collection is performed to determine urine waste). A breath test with oral xylose exists as H2-xylose test, with administration of labeled xylose such as 14C-xylose or 13C-xylose test. Xylose is further metabolized by bacteria in the small and large intestine, so the decrease in absorption, determined mainly by the classical tolerance test, is diagnostically significant for malabsorption, while increased metabolism of xylose is detectable by bacterial overgrowth in the small intestine. The indication for the xylose breath test is therefore mainly syndrome of bacterial overgrowth, blind loops syndrome, etc. The dose of xylose administered varies from 10 mg to 10 g (depending on the test design).

 'Performing a test'  in our lab is as follows. The patient takes an exhaled air sample on an empty stomach, drinks a 200 ml solution of 100 mg of C-xylose, and one exhaled air sample is taken every 60 minutes for the next 6 hours. The evaluation is kinetic, we evaluate the maximum achieved ratio 13 CO 2: 12 CO 2, the time shift of the maximum, and the total the amount of metabolized 13 C-xylose by the so-called cumulative release in 6 hours.

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