Assay of urinary oxalate: six methodologies compared

To assess how well results by different methods for urinary oxalate determinations agree with each other in a clinical setting, we compared six different assays: Hodgkinson and Williams (Clin Chim Acta 36:127-132, 1972), enzymatic, modified Hodgkinson and Williams, gas chromatography, ion chromatography, and "high-pressure" liquid chromatography. For the entire group of samples, the mean value by each method agreed relatively closely, although the enzymatic procedure produced a somewhat higher value. All six methods had large coefficients of variation within (8-58%) and between (15-88%) assays. In addition, analytical recovery by most assays was more than 100% of the added oxalate. Analytical recovery of 10 micrograms of oxalate added per milliliter of urine specimen ranged from 86 to 237%; for 20 micrograms/mL it was 83 to 320%. Thus for the six methods evaluated, no single method appeared to be superior to the others.