Improvement and Validation of d‐Xylose Determination in Urine and Serum as a New Tool for the Noninvasive Evaluation of Lactase Activity in Humans

Abstract

The modified method provides high sensitivity and robustness for d-xylose quantification in urine/serum for routine clinical use especially in the noninvasive diagnosis of intestinal lactase deficiency with the gaxilose test.

Development of a new method for d-xylose detection and quantification in urine, based on the use of recombinant xylose dehydrogenase from Caulobacter crescentus

“…In this study, quantification of xylose amounts in urine after the administration of placebo (water) to 12 healthy volunteers yielded a mean value of 12.92 ± 5.26 mg (Hermida et al, 2013), suggesting the presence of an interfering component in some urine samples. On the other hand, the linear range for the colorimetric method using phloroglucinol was found to be 0.5 to 20 mg/dL, being slightly wider than that obtained with the enzymatic method (0.1 to 15 mg/dL) (Hermida et al, 2014).…”

Analytical Validation of a New Enzymatic and Automatable Method for d-Xylose Measurement in Human Urine Samples

“…Even though the analytical sensitivity of the latter was slightly better, with a LoQ of 0.46 mg/dL [19], the new enzymatic assay has the advantages of being automatable, not requiring the use of acids and heat, and avoiding possible errors due to sample manipulation. Furthermore, it represents the first enzymatic xylose quantification technique that has been validated and will facilitate the use of the gaxilose test in the clinical practice.…”

“…Since this method was not sensitive enough to detect the low amounts of xylose present in urine and blood after the oral ingestion of gaxilose, some modifications were introduced in the assay protocol. The resulting method was validated and was proved to be very sensitive and reliable [ 19 ]. Nevertheless, this methodology has represented a barrier for the use of the gaxilose test, since most of clinical laboratories are fully automated and reluctant to include any new manual analytical technique.…”

Phase IV noninferiority controlled randomized trial to evaluate the impact on diagnostic thinking and patient management and the test–retest reproducibility of the Gaxilose test for hypolactasia diagnosis

“…There, xylose quantification in 0 to 4 hours and 4 to 5 hours urine samples was conducted by the phloroglucinol colorimetric reaction described in the GT SmPC. [15,16] A total xylose amount in the urine collected from 0 to 5 hours after Gaxilose administration lower than 37.87 mg was indicative of hypolactasia diagnosis.…”

“…The total xylose amount excreted in the urine collected from 0 to 4 hours of the Gaxilose test and retest was quantified by the phloroglucinol method as previously reported. [15,16] The reproducibility was evaluated through the intraclass correlation coefficient (ICC) and through the agreement Kappa coefficient, [17–19] taking into account that the cut-off of the total xylose amount in urine accumulated from 0 to 4 hours is 27.58 mg. [7,8] Therefore, patients with a xylose amount lower than this value would be considered hypolactasic.…”