In Vitro Synthesis of Oxalic Acid Has No Relevant Influence on Plasma Oxalic Acid Levels in Haemodialysis Patients

Abstract

Plasma oxalic acid concentrations were measured in 13 chronic hemodialysis patients. The mean plasma oxalic acid concentration was 128.0 .+-. 48.6 .mu.mol/l, being .apprx. 8 times higher than the plasma concentration of 14 volunteers (.hivin.x = 16.8 .+-. 5.2 .mu.mol/l). Ultrafiltrates obtained in vivo from these patients showed a mean oxalic acid concentration of 138.2 .+-. 56.5 .mu.mol/l. Since in vivo ultrafiltrates are free of erythrocytes and plasma enzymes, an in vitro synthesis of oxalic acid from precursors by erythrocytes and plasma enzymes can be excluded. As the oxalic acid concentration of plasma corresponded to that of in vivo ultrafiltrates, any in vitro formation of oxalic acid in hemodialysis patients must be negligibly small, and is irrelevant for the measurement of plasma oxalic acid levels in patients receiving regular hemodialysis.