A simple, rapid assay for plasma oxalate in uraemic patients using oxalate oxidase, which is free from vitamin C interference.

An enzymatic assay for the determination of oxalate in plasma was developed which is specific, simple, rapid and requires no specialised equipment; interference from vitamin C was removed by incubation of acidified plasma ultrafiltrate with ascorbate oxidase prior to oxalate estimation. Recoveries were 93 +/- 11% and the inter-batch coefficient of variation for 31 determinations at an oxalate level of 24 mumol/l was 10%. The assay is linear up to 300 mumol/l with a detection limit of 2 mumol/l. The reference range, based on results from 25 healthy volunteers, was defined as less than 2-5 mumol/l which is similar to levels established for the in vivo isotope dilution technique. The assay has an added advantage over the latter method, which requires a urine collection, in that it can be applied to plasma from anuric patients. A linear correlation (r = 0.68, p less than 0.001) was found between plasma oxalate and serum creatinine in individuals with varying degrees of renal failure.