title: 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: BACKGROUND
  The phloroglucinol assay is the current method for d-xylose determination in urine/plasma/serum. However, its sensitivity is limited when low amounts of d-xylose are to be measured, such as in the noninvasive evaluation of intestinal lactase with 4-galactosylxylose (gaxilose). An improved assay was therefore needed.
  
  
  METHODS
  We developed and validated a modified version of the phloroglucinol-based assay for quantification of d-xylose in urine/serum samples. A method for gaxilose determination by gas chromatography (GC) was also optimized.
  
  
  RESULTS
  Linearity ranged from 0.125 to 5.0 mg/l (5-200 mg/l in original sample). Accuracy at LOQ (0.125 mg/l) was 0.97/2.49% in spiked urine/serum; for other quality controls (QC), it was <1.27%. Intra- and interassay precision at LOQ were 6.02% and 6.45% for urine, and 8.86% and 10.00%, respectively, for serum; for other QC, precision was <2.15%. Linearity of gaxilose determination by GC was 3.90-195.17 for urine and 9.75-195.17 mg/l for serum with acceptable sensitivity and reproducibility. The method proved adequate for the d-xylose determination in healthy and hypolactasic subjects after oral administration of gaxilose.
  
  
  CONCLUSIONS
  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.
authors.affiliation: Departamento de Bioquímica and Instituto de Investigaciones Biomédicas Alberto Sols, Facultad de Medicina de la Universidad Autónoma de Madrid, Universidad Autónoma de Madrid-Consejo Superior de Investigaciones Científicas, Madrid, Spain; Venter Pharma SL, Madrid, Spain.
authors.forename: Carmen
authors.initials: C
authors.lastname: Hermida
authors.forename: Oscar H
authors.initials: OH
authors.lastname: Martínez-Costa
authors.forename: Guillermo
authors.initials: G
authors.lastname: Corrales
authors.forename: Cristina
authors.initials: C
authors.lastname: Teruel
authors.forename: Valentina
authors.initials: V
authors.lastname: Sánchez
authors.forename: José J
authors.initials: JJ
authors.lastname: Sánchez
authors.forename: Dolores
authors.initials: D
authors.lastname: Sarrión
authors.forename: María J
authors.initials: MJ
authors.lastname: Ariza
authors.forename: Rosa
authors.initials: R
authors.lastname: Codoceo
authors.forename: Idoya
authors.initials: I
authors.lastname: Calvo
authors.forename: Alfonso
authors.initials: A
authors.lastname: Fernández-Mayoralas
authors.forename: Juan J
authors.initials: JJ
authors.lastname: Aragón
mesh_terms: D002849:Chromatography, Gas / Q000379:methods; D003124:Colorimetry / Q000379:methods*; D004187:Disaccharides / Q000097:blood / Q000737:chemistry / Q000378:metabolism* / Q000652:urine; D006801:Humans; D043322:Lactase / Q000378:metabolism*; D010696:Phloroglucinol / Q000737:chemistry; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D014994:Xylose / Q000097:blood / Q000737:chemistry / Q000378:metabolism* / Q000652:urine
chemical_list: D004187:Disaccharides; C073827:4-O-galactopyranosylxylose; D014994:Xylose; D010696:Phloroglucinol; D043322:Lactase
keywords: 4-galactosylxylose; analytical validation; d-xylose; gaxilose; hypolactasia; intestinal lactase; phloroglucinol