title: Oxalic Acid as a uremic toxin.
abstract: OBJECTIVE
  Oxalic acid (OA) is thought to be a uremic toxin that participates in the pathogenesis of uremic syndrome. The objectives of this study were to: (1) evaluate the plasma levels of OA in patients with chronic renal disease with various levels of glomerular filtration rate and after renal transplantation; (2) investigate the salivary secretion of OA and ascorbic acid in healthy subjects and in patients with chronic renal failure (CRF); (3) examine the influence of water and sodium diuresis and furosemide administration on the urinary excretion of OA and ascorbic acid in healthy subjects and in CRF patients without dialysis treatment; and (4) evaluate the influence of renal replacement therapy (RRT) on secondary hyperoxalemia in hemodialysis patients.
  
  
  METHODS
  This study was conducted at the Nephrological Department of P.J. Safárik University. Sixty-one patients with chronic renal disease, 64 CRF patients, 32 continuous ambulatory peritoneal dialysis (CAPD) patients, 15 hemodialysis patients, 21 patients after renal transplantation, and 15 healthy subjects were examined. Maximal water diuresis, diets with low (2 g/day) and high (15 g/day) sodium intake, administration of intravenous furosemide (20 mg), and renal replacement therapy (CAPD, hemodialysis, hemofiltration, and postdilution hemodiafiltration) were utilized in the study.
  
  
  RESULTS
  In patients with chronic renal disease and those after renal transplantation, direct relationships between plasma OA and serum creatinine were found (r = 0.904 and 0.9431, respectively, P < .01). Despite a high level of plasma OA in uremic patients (23.1 +/- 10 micromol/L), there was no significant difference in salivary OA between control subjects (128 +/- 19 micromol/L) and CRF patients (135 +/- 24 micromol/L). The urinary excretion of OA during maximal water diuresis (from 37.5 to 110.3 micromol/4 hours) and after intravenous furosemide (from 34.5 to 66.7 micromol/3 hours) increased significantly, but was not affected by high intake of NaCl. The most significant decrease of plasma OA was observed during postdilution hemodiafiltration (63.3%).
  
  
  CONCLUSIONS
  Our study indicates that renal replacement therapy is not effective for a permanent reduction of elevated plasma levels of OA.
authors: Nephrological Clinic, Medical School of P.J. Safárik University, Kosice, Slovak Republic.
authors: Miroslav
authors: M
authors: Mydlík
authors: Katarína
authors: K
authors: Derzsiová
mesh_terms: D000328:Adult; D001205:Ascorbic Acid / Q000097:blood; D050197:Atherosclerosis / Q000453:epidemiology; D003404:Creatinine / Q000097:blood; D005260:Female; D005921:Glomerulonephritis / Q000097:blood; D006801:Humans; D007674:Kidney Diseases / Q000097:blood / Q000139:chemically induced* / Q000453:epidemiology; D007676:Kidney Failure, Chronic / Q000097:blood / Q000139:chemically induced* / Q000453:epidemiology / Q000628:therapy; D016030:Kidney Transplantation / Q000009:adverse effects / Q000502:physiology; D008297:Male; D008875:Middle Aged; D019815:Oxalic Acid / Q000097:blood / Q000633:toxicity*; D010531:Peritoneal Dialysis, Continuous Ambulatory; D006435:Renal Dialysis; D014511:Uremia / Q000139:chemically induced*; D025101:Vitamin B 6 / Q000627:therapeutic use
chemical_list: D025101:Vitamin B 6; D019815:Oxalic Acid; D003404:Creatinine; D001205:Ascorbic Acid