Determination of plasma oxalate with chloride ion insensitive oxalate oxidase

A simple colorimetric method has been developed for determination of oxalate in plasma using a C1-insensitive oxalate oxidase purified from grain sorghum leaves. The ultrafiltered plasma collected in 3.5 N HC1 was pretreated with NaNO2 to avoid possible interference by ascorbate. The minimum detection limit of the method is 0.225 mg/l. The % recovery of the added oxalate was 91.5 +/- 5.0 (mean +/- S.D., n = 15). The coefficient of variation within and between batch were < 3 and < 5 respectively. The mean plasma oxalate concentration in healthy subjects was 0.29 mg/l. The method has the advantage over other enzymic methods that it doesn't require the removal of C1- prior to oxalate assay.