Abstract
Many authors have studied the influence of storage on measured albumin concentrations in urine. Whereas some authors report that albumin concentrations decrease upon storage of urine at −20 °C (1)(2)(3)(4)(5)(6)(7)(8)(9)(10), others cannot confirm this (11)(12)(13)(14). As has been discussed extensively in the literature (15), these seemingly discrepant results might be explained by the use of pooled urine vs individual urine samples. The effect of storage may differ between various urine samples, probably because of variables such as protein concentrations, pH, and ionic strength. As a consequence, pooling of the urine samples might dilute the storage effect that can be found when using individual urine specimens. Other variables that have been tested for their influence on the measurements of urinary proteins are pH (1)(2)(3)(4)(13)(16)(17)(18), the tube material (4)(19)(20), handling of the sample (1)(7)(10)(12)(14), and the use of additives (21)(22)(23). It is likely that proteins other than albumin are also influenced by storage conditions, but information about the extent of such effects is limited (1)(3)(16)(17)(18)(21)(22)(23). In the study presented here, we measured several urinary proteins by nephelometry [albumin, transferrin, IgG, and α1-microglobulin (α1-m)] or by an RIA [β2-microglobulin (β2 …
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