How and how long to store urine samples before albumin radioimmunoassay: a practical response

Abstract

We used three study protocols to check the dependence of albumin stability, measured by an RIA, on different temperatures, durations, and materials (i.e., assay tubes) of urine storage. Albumin values obtained for samples stored in three types of assay tubes (glass, polystyrene, and polypropylene) throughout the 2 months of the first (prospective) protocol were superimposable. The 24-h storage of six urine samples at room temperature or at 4 degrees C, as well as 72-h storage at 4 degrees C, did not affect the albumin measurement by RIA. After 2 months of storage of these same six urine samples at -20 degrees C, there was still no albumin decrease. A significant albumin decrease occurred (a mean of approximately 5% per year, throughout the range of albumin concentrations tested) when samples stored at -20 degrees C were reassayed by RIA after > or = 2 years (second protocol, retrospective). Finally, 3 of 21 (14.3%) urine pools stored at -20 degrees C for various periods (4-21 months) showed a significant albumin loss after storage; the time of storage as well the decrement rates of these 3 pools differed from each other (third protocol, retrospective). Short- and medium-term (2-6 months) freezing of urine samples at -20 degrees C does not significantly affect the stability of immunoreactive albumin. For longer preservation periods, storage of urine samples at -70 degrees C may be preferable.

Consecutive First-Morning Urine Samples to Measure Change in the Albumin-to-Creatinine Ratio: A Pilot Study of a Home Urine Collection Protocol

“…We found that delaying the laboratory analysis of samples by 24–48 h (stored at 4 °C) did not affect the results; however, delaying the analysis by 3–9 months (stored at −80 °C) resulted in a systematic overestimation of ACR of approximately 8 %. The latter observation contrasts to previous studies which found either no change in ACR [ 23 – 25 ] or a 10 % decrease after long-term storage of frozen samples [ 26 – 28 ]. While a detailed investigation into the effects of sample processing on ACR measurement was beyond the scope of this study, others have shown that laboratory assay parameters (which are not standardized across laboratories) can affect ACR measurement.…”

Urinary proteases degrade albumin: implications for measurement of albuminuria in stored samples

“…Previous studies have measured the stability of albumin in frozen samples, with mixed results. Numerous studies have found negligible effect of freezing on urinary albumin concentration 1–3 while others have found considerable albumin losses. 4–9 The use of stored samples for albuminuria research has been criticized due to the potential for long-term degradation of albumin in stored urine.…”

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].…”