STABILITY OF FREE PROSTATE-SPECIFIC ANTIGEN IN SERUM SAMPLES UNDER A VARIETY OF SAMPLE COLLECTION AND SAMPLE STORAGE-CONDITIONS

Objectives. Four studies were conducted to characterize the stability of free and total prostate specific antigen (PSA) under various sample collection and storage conditions. Methods. In the first study, fresh blood from 11 patients was drawn and allowed to clot at room temperat ure (RT). Serum was prepared by centrifugation 1, 3, 5, or 8 hours aft er the blood draw and tested to determine the free and total PSA level s. In the second study, serum specimens from 12 individuals were store d at RT or 4 degrees C and were tested on days 0, 1, 2, and 7. In the third study, four fresh serum samples were subjected to five freeze-th aw cycles and tested after each cycle. In the fourth study, 29 fresh s amples were aliquoted, frozen at -20 degrees C or -70 degrees C, and m onitored for long-term stability. Results. Approximately 1% of the fre e PSA was lost per hour of clotting time. Between 2% and 5% of the fre e PSA was lost per day of storage at 4 degrees C or 23 degrees C. Abou t 0.9% of the free PSA was lost per month of storage at -20 degrees C compared with about 0.4% per month at -70 degrees C. Total PSA appeare d to be stable throughout these studies. Conclusions. Our results sugg est that routine serum preparation and refrigerated storage of samples for up to 24 hours is acceptable for the measurement of both free and total PSA. Samples that are to be retained for longer than 24 hours s hould be frozen. Samples stored for extended periods should be kept at -70 degrees C. Copyright 1996 by Elsevier Science Inc.