2-YEAR STABILITY OF FREE AND TOTAL PSA IN FROZEN SERUM SAMPLES

Objectives. To investigate the stability of free and total prostate-sp ecific antigen (PSA) in serum stored at -20 degrees C and -70 degrees C for 2 years. Methods. Fresh blood from 29 patients was drawn and all owed to clot at room temperature. Serum was prepared by centrifugation 1 hour later and tested to determine the free and total PSA levels. S amples were aliquoted, frozen at -20 degrees C or -70 degrees C, and m onitored for long-term stability over the course of 2 years. Results. On average, 91% of the free PSA, 92% of the total PSA, and 89% of the percent free PSA values were recovered after 2 years of storage at -20 degrees C; and 96% of the free PSA, 101% of the total PSA, and 95% of the percent free PSA values were recovered after 2 years of storage a t -70 degrees C. Seventy percent of the samples stored at -20 degrees C and 100% of the samples stored at -70 degrees C showed no statistica lly significant decline in free PSA values over the 2-year period. Onl y one total PSA sample (-20 degrees C) showed a statistically signific ant loss after 2 years of storage. Conclusions. Our results suggest th at samples stored frozen for up to 2 years at -70 degrees C should giv e acceptable percent free PSA results. UROLOGY 52: 247-251, 1998. (C) 1998, Elsevier Science Inc. All rights reserved.