STUDIES ON OXALATE IN UROLITHIASIS

IV. Plasma Oxalate in Oxalate Stone Formers

Abstract

The present assay for oxalate in plasma is a modification of the radioenzymatic isotope-dilution technique developed by D. J. Bennett et al. The oxalate in 5ml of plasma ultrafiltrate is purified by precipitation and ex-traction. The enzyme assay is carried out in a 0.2ml reaction mixture, so that the assay sensitivity is increased up to 0.3μg of anhydrous oxalate. The mean oxalate concentration from 15 apparently healthy subjects who had fasted overnight was 15.9±10.8μmol/l (SD), while that from 15 calcium oxalate stone-formers was 27.6±7.2μmol/l.
It was suspected that the latter value might be too high, possibly due to the conversion of glyoxalate to oxalate, as has been pointed out by T. Ackay et al. Inhibitors of the glyoxalate oxidation were, therefore, added to the freshly taken blood samples. The mean oxalate concentration with the inhibitors from the controls was 14.3±5.1pmol/l (SD), while that with the inhibitors from the stone-formers was 12.1±4.5pmol/l (SD). It is likely that normal blood spontaneously generates oxalate on standing.
It is concluded that there is no significant difference in plasma oxalate concentration between the two groups, nor any sex-dependent differences, as determined by means of a sensitive, specific, and accurate assay, with inhibitors used in order to prevent the enzymatic conversion of glyoxalate to oxalate.