title: Urinary oxalate determination by use of immobilized oxalate oxidase in a continuous-flow system.
abstract: In this procedure, oxalate oxidase (EC 1.2.3.4) immobilized in a continuous-flow system is used to determine oxalate in urine. The hydrogen peroxide formed from oxalate is detected by use of a color reaction with peroxidase (EC 1.11.1.7), 3-methyl-2-benzothiazoline hydrazine, and N,N-dimethylalanine. However, urine contains an oxalate oxidase inhibitor, which cannot be removed by heating, ion-exchange resins, or cellulose columns. This makes it necessary to precipitate the oxalate before assay. The overall assay system is accurate (oxalate recovery, 95.9%), sensitive (less than or equal to 5 mumol/L), precise (within-batch CV less than 1.25%, between-batch CV less than 5%), and relatively rapid (60 samples per working day). The assay system has better accuracy than an established chemical method and a gas-chromatographic method, and is considerably less arduous than and correlates well (r = 0.94) with a modified chemical method. The reference interval for urinary oxalate excretion is 0.16-0.56 mmol per day (n = 97). Only nonphysiological concentrations of ascorbate interfere with the assay, by increasing the oxalate result in the overall assay, presumably by post-micturition formation of oxalate from ascorbate in the urine samples.
mesh_terms: D000328:Adult; D000368:Aged; D001322:Autoanalysis / Q000379:methods; D004800:Enzymes, Immobilized / Q000037:antagonists & inhibitors; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D010070:Oxalates / Q000652:urine*; D010088:Oxidoreductases / Q000037:antagonists & inhibitors
chemical_list: D004800:Enzymes, Immobilized; D010070:Oxalates; D010088:Oxidoreductases