Effects of storage time and temperature on measurement of small concentrations of albumin in urine

Abstract

Accurate measurement of albumin excretion rates is important in choosing treatment regimens that may reverse early diabetic renal damage. We report here determinations of slight albuminuria ("microalbuminuria") by radioimmunoassay of fresh specimens, frozen aliquots (stored at -20 degrees C for two, eight, and 24 weeks), and refrigerated specimens (stored at 4 degrees C for one, two, and eight weeks). Seven separate analyses were performed on 101 specimens of urine obtained from 37 subjects with insulin-dependent diabetes mellitus and from 10 nondiabetic healthy controls of a similar age. Storage of urine samples at -20 degrees C resulted in significantly lower measurements of microalbuminuria than in fresh urine (ANOVA, corrected for repeated measures: P = 0.01 to 0.0001). In contrast, storage of urine samples at 4 degrees C for as long as eight weeks did not significantly affect urinary albumin results. The pH values of the specimens were minimally altered and were not a likely cause of the decreased albumin values in the frozen specimens. We conclude that urine specimens for microalbuminuria measurements should either be analyzed as fresh specimens or stored at 4 degrees C and assayed as soon as possible.

Freezing method affects the concentration and variability of urine proteins and the interpretation of data on microalbuminuria

“…As storage at 4°C was not a practical option in the ORPS study, the question of how this compares with storage at −20°C or −70°C was not addressed. However, recent studies show that albumin is preserved for least 7 days if stored at 4°C[19–29]. Furthermore, specimen storage at −70°C for 3 months in comparison with specimens analysed fresh did not affect urine proteins[18].…”

Alkalinization of urine samples preserves albumin concentrations during prolonged frozen storage in patients with diabetes mellitus

“…The advantages are increased control on logistics and prevention of analytical day-to-day variation and drift. Although some studies found no effect of frozen storage on UAC [6][7][8], others found erroneously low values, in particular if storage was for 6 months or longer [9][10][11][12]. Importantly, the decline in UAC during frozen storage has been reported to vary greatly between samples, making the decline for an individual sample very unpredictable [13,16].…”

Influence of biological variations and sample handling on measured microalbuminuria in diabetic patients

“…Correlaa significant decrease of albumin concentration in frozen samples (1 1,13, IS), while others did not find significant effects (9,12). Storage at room temperature for I week or at 4°C for 3 weeks caused no significant changes (13,15). It has been suggested also that urine pH is important in the formation of precipitate leading to a decreased albumin concentration in urine samples (10).…”

“…analyser because we found this assay inexpensive, simple, and rapid to perform, and it fits into our laboratory organisation. The choice of the sample and the way of the handling of the sample is much more disputable (6)(7)(8)(9)(10)(11)(12)(13)(14)(15)(16). There is a general agreement that 24 h collection is the most reliable specimen to confirm the presence of microalbuminuria (6,14,16).…”