Development of a reference method for determining urinary oxalate by means of isotope dilution—mass spectrometry (ID-MS) and its usefulness in testing existing assays for urinary oxalate

An accurate and reproducible GC-MS reference method for determining urinary oxalate is presented. With forty 24-h urines, comparisons were made between this reference method and four other existing procedures: a GC method, an HPLC method and two enzymatic assays. The results of the first two methods were in accordance with the GC-MS method. The performance of the enzymatic kits was less satisfactory. The use of a GC-MS reference method in evaluating existing and newly developed methods is recommended.