Renal stone disease is an important medical problem and calcium oxalate is the major component of most calculi. Although assays of urinary calcium are commonly performed, oxalate is not often measured even though it is much more influential in determining the degree of supersaturation of urine than calcium. This might be because the assay of oxalate has not been easy. However, an improved method that has recently become available is practical, inexpensive and overcomes previous shortcomings. Before any new assay is introduced, knowledge should be available on desirable performance standards, the utility of conventional population-based reference intervals and the significance of changes in serial results obtained on an individual. Information on these and other aspects can be obtained simply by generation and application of data on analytical, within-subject and between subject components of variation over the short term on a small cohort of subjects. Our aim was to obtain this information and generate useful indices for first morning and random specimens as well as 24 h urine specimens since the former are easier to collect, and to assess whether correction for urine flow by use of creatinine concentrations was likely to be useful. Previous studies have simply indicated that oxalate is very variable in individuals.
