title: Interference-free sample preparation for the determination of plasma oxalate analyzed by HPLC-ER: preliminary results from calcium oxalate stone-formers and non-stone-formers.
abstract: BACKGROUND
  Oxalate generation at pH-values above 5.0 and an oxalate-protein binding in acidified plasma would appear to complicate the determination of oxalate in plasma.
  
  
  METHODS
  To avoid complex sample preparation we used a high-performance liquid chromatographic system with an inline enzyme reactor (HPLC-ER) containing immobilised oxalate oxidase. The detection limit was 0.68 micromol/l. Blood was drawn in lithium-heparin vessels and immediately centrifuged at 4 degrees C. The yielded plasma was ultrafiltered using a Centrisart-I-tube. To inhibit oxalate generation by ascorbic acid, the ultrafiltrate was acidified with 1 mol/l hydrochloric acid during ultrafiltration at 4 degrees C. The liquid thus yielded was used for HPLC-ER analysis. Blood samples were obtained from 133 healthy adults (63 men, 70 women, aged 20-94 years) with no history of renal disorder and from 79 patients (53 men, 26 women, aged 19-77 years) with a history of calcium oxalate stone formation.
  
  
  RESULTS
  Mean plasma oxalate was 2.65 +/- 2.31 micromol/l for healthy subjects and 4.21 +/- 0.56 micromol/l for stone formers.
  
  
  CONCLUSIONS
  Analysis yielded no significant differences between males and females. A correlation between age and plasma oxalate was found for the healthy adults (p < 0.001).
authors.affiliation: Division of Experimental Urology, Department of Urology, University of Bonn, Klinik und Poliklinik fur Urologie, Sigmund-Freud-Str. 25, 53 105, Bonn, Germany.
authors.forename: Ruth
authors.initials: R
authors.lastname: Hönow
authors.forename: A
authors.initials: A
authors.lastname: Simon
authors.forename: A
authors.initials: A
authors.lastname: Hesse
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D001205:Ascorbic Acid / Q000737:chemistry; D002129:Calcium Oxalate / Q000097:blood*; D002851:Chromatography, High Pressure Liquid; D004800:Enzymes, Immobilized; D005260:Female; D006801:Humans; D007202:Indicators and Reagents; D007669:Kidney Calculi / Q000097:blood*; D008297:Male; D008875:Middle Aged; D010070:Oxalates / Q000097:blood*; D010088:Oxidoreductases / Q000737:chemistry; D011485:Protein Binding; D014462:Ultrafiltration
chemical_list: D004800:Enzymes, Immobilized; D007202:Indicators and Reagents; D010070:Oxalates; D002129:Calcium Oxalate; D010088:Oxidoreductases; C020598:oxalate oxidase; D001205:Ascorbic Acid