Studies of diabetic nephropathy. I. Effects of storage time and temperature on microalbuminuria

The effect of storage time and temperature on the immunological turbidimetric measurement of a low concentration of albumin in urine was investigated. In storage at -20 degrees C, the albumin level decreased, but the rate of this decrease differed considerably among specimens. However, under storage at room temperature for 2 weeks, or at 4 degrees C for 5 weeks albumin levels did not show significant changes. At -40 degrees C and -80 degrees C there were only slight decreases. At -40 degrees C decreases were slightly greater than at -80 degrees C. Therefore, -80 degrees C was found to be the optimal temperature for long-term storage of urinary albumin. Some of the specimens showed a 50% decrease in albumin level after storage for 9 weeks at -20 degrees C, but remained unchanged after storage for the same period at -80 degrees C. A pair of specimens preserved at -20 degrees C and -80 degrees C were isolated by SDS-PAGE (sodium dodecyl sulfate-polyacrylamide gel electrophoresis). After electrophoresis, urinary proteins were stained by silver staining to observe bands, and albumin content was determined by immunoblotting. A decrease in albumin concentration was also observed by densitometric detection.