title: The oxalate level in ultrafiltrate fluid collected from a dialyzer is useful for estimating the plasma oxalate level in hemodialysis patients.
abstract: BACKGROUND
  Patients on chronic hemodialysis are likely to develop secondary hyperoxalemia. It is, however, difficult to measure plasma oxalate levels. To measure plasma oxalate levels, rapid plasma separation, deproteinization, and acidification are essential in preventing the formation of oxalate and the deposition of calcium oxalate within the test tube. The present study was undertaken to examine whether the oxalate level in dialyzer ultrafiltrate is potentially useful for estimating plasma oxalate levels.
  
  
  METHODS
  In nine patients on chronic hemodialysis, the plasma, after deproteinization with a filter, and the ultrafiltrate from the dialyzer before hemodialysis were acidified to a pH level of less than 3, followed by the measurement of oxalate levels by ion chromatography. Also, oxalate levels were compared between acidified and non-acidified ultrafiltrates from the dialyzer. In the second part of the study, seven patients on chronic hemodialysis receiving erythropoietin therapy, in whom the ferritin level was more than 300 ng/ml and transferrin saturation was less than 25%, were intravenously administered ascorbic acid, 100 mg, three times a week, after each dialysis session to facilitate the utilization of stored iron. This treatment was continued until the serum ferritin level decreased to a level below 300 ng/ml (for 3 months, at a maximum). The oxalate level in the dialyzer ultrafiltrate after this treatment was compared with that before treatment.
  
  
  RESULTS
  The mean +/- SE oxalate level in the dialyzer ultrafiltrate was 45 +/- 6 micromol/l, essentially equal to the plasma oxalate level (46 +/- 7 micromol/l). The plasma oxalate level had a significant positive correlation with the dialyzer ultrafiltrate oxalate level (plasma oxalate level = 0.99 x dialyzer ultrafiltrate oxalate level + 1.5; r = 0.95; P < 0.0001). The oxalate level in the acidified ultrafiltrate (45 +/- 6 micromol/l) did not differ significantly from that in the non-acidified ultrafiltrate (45 +/- 6 micromol/l). The mean +/- SE duration of ascorbic acid administration was 64 +/- 13 days. The hemoglobin level remained unchanged at 9.6 +/- 0.4 g/dl, whereas the serum iron level increased significantly, from 34 +/- 2 microg/dl to 43 +/- 4 microg/dl (P < 0.05), and serum ferritin levels decreased significantly, from 645 +/- 219 ng/ml to 231 +/- 30 ng/ml after the treatment (P < 0.05). The oxalate level in the acidified ultrafiltrate showed no significant change after ascorbic acid administration (31 +/- 8 micromol/l vs 47 +/- 7 micromol/l).
  
  
  CONCLUSIONS
  In patients on chronic hemodialysis, the oxalate level in acidified ultrafiltrate from the dialyzer was found to be useful for estimating the plasma level of non-protein-bound oxalate. When administering ascorbic acid to hemodialysis patients, the plasma oxalate level can be monitored using this method.
authors.affiliation: Department of Internal Medicine, Yuurinkouseikai Fuji Hospital, 1784 Niihashi, Gotemba, Shizuoka 412-0043, Japan. ogi@yuurinkouseikai.or.jp
authors.forename: Makoto
authors.initials: M
authors.lastname: Ogi
authors.forename: Ryoetsu
authors.initials: R
authors.lastname: Abe
authors.forename: Tomohito
authors.initials: T
authors.lastname: Nishitani
authors.forename: Masanori
authors.initials: M
authors.lastname: Wakabayashi
authors.forename: Tsunemichi
authors.initials: T
authors.lastname: Wakabayashi
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D001205:Ascorbic Acid / Q000627:therapeutic use; D004921:Erythropoietin / Q000627:therapeutic use; D005260:Female; D017583:Hemodiafiltration / Q000009:adverse effects; D015312:Hemodialysis Solutions / Q000737:chemistry*; D006801:Humans; D006863:Hydrogen-Ion Concentration; D008297:Male; D008875:Middle Aged; D010070:Oxalates / Q000032:analysis* / Q000097:blood*; D011994:Recombinant Proteins
chemical_list: D015312:Hemodialysis Solutions; D010070:Oxalates; D011994:Recombinant Proteins; D004921:Erythropoietin; D001205:Ascorbic Acid