STUDIES OF DIABETIC NEPHROPATHY .1. EFFECTS OF STORAGE TIME AND TEMPERATURE ON MICROALBUMINURIA

The effect of storage time and temperature on the immunological turbid imetric measurement of a low concentration of albumin in urine was inv estigated. In storage at -20 degrees C, the albumin level decreased, b ut the rate of this decrease differed considerably among specimens. Ho wever, under storage at room temperature for 1 weeks, or at 4 degrees C for 5 weeks albumin levels did not shea significant changes. At -40 degrees C and -80 degrees C there were only slight decreases. At -40 d egrees C decreases were slightly greater than at -80 degrees C. Theref ore, -80 degrees C was found to be the optimal temperature for long-te rm storage of urinary albumin. Some of the specimens showed a 50% decr ease 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 elect rophoresis). After electrophoresis, urinary proteins were stained by s ilver staining to observe bands, and albumin content was determined by immunoblotting. A decrease in albumin concentration was also observed by densitometric detection.