Measurement of plasma oxalate in healthy subjects and in patients with chronic renal failure using immobilised oxalate oxidase

Abstract

A continuous flow assay using immobilised oxalate oxidase was used to measure the level of oxalate in plasma ultrafiltrate obtained from healthy subjects and from patients with chronic renal failure. The levels of oxalate in plasma from normal subjects ranged from 1.3–3.1 μmol/l (mean 2.03; sd = 0.52) with fe0males showing a higher ( p < 0.05) level (mean 2.25 μmol/l) than males (mean 1.87 μmol/l). The mean oxalate/creatinine clearance ratio in fourteen healthy subjects was greater than unity, thus indicating a net tubular secretion of oxalate. At physiological pH, l-ascorbate was converted to oxalate in whole blood following venepuncture, in plasma and in plasma ultrafiltrate. Reduction of the spontaneous generation of oxalate in the samples prior to analysis was achieved by acidification and treatment with sodium nitrite. A linear correlation ( r = 0.92; p < 0.001) was found between plasma oxalate and plasma creatinine in patients with chronic renal failure.