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Received on April 24, 2005
Accepted on December 5, 2005
Cancer Diagnostics |
1 Department of Laboratory Medicine, Division of Clinical Chemistry, Lund University, University Hospital (UMAS), Malmö, Sweden
2 Department of Internal Medicine, Lund University, University Hospital (UMAS), Malmö, Sweden
3 Schering Oy, Turku, Finland
4 Department of Urology, Lund University, University Hospital (UMAS), Malm|$$|Ado, Sweden
5 Department of Urology, Sahlgrenska University Hospital, Göteborg, Sweden
6 Department of Laboratory Medicine, Division of Clinical Chemistry, and Departments of Clinical Laboratories, Urology, and Medicine, Memorial Sloan-Kettering Cancer Center, New York, NY
* To whom correspondence should be addressed. E-mail: David.Ulmert{at}med.lu.se.
Background: Long-term frozen storage may alter the results of prostate-specific antigen (PSA) measurements, mainly because of degradation of free PSA (fPSA) in vitro. We compared the effects of long-term storage on fPSA, total PSA (tPSA), and complexed PSA (cPSA) in serum vs EDTA-plasma samples.
Methods: We measured fPSA and tPSA concentrations in matched pairs of archival serum and EDTA-plasma samples (stored frozen at -20 °C for 20 years) from a large population-based cohort in Malmö, Sweden. We also compared concentrations in age-matched men with those in samples not subjected to long-term storage, obtained from participants in a population-based study of prostate cancer screening in Göteborg, Sweden. These contemporary samples were handled according to standardized preanalytical and analytical protocols aimed at minimizing in vitro degradation. tPSA and fPSA measurements were performed with a commercial assay (Prostatus Dual Assay; Perkin-Elmer Life Sciences).
Results: Concentrations of tPSA and fPSA and calculated cPSA (tPSA - fPSA) in archival plasma were not significantly different from those in contemporary serum from age-matched men. In archival serum, however, random variability of fPSA was higher vs plasma than in contemporary samples, whereas systematic error of fPSA analyses was similarly small in archival and contemporary serum and plasma.
Conclusions: Concentrations of tPSA and calculated cPSA were highly stable in plasma and serum samples subjected to long-term storage at -20 °C. Greater random variability, rather than a systematic decrease, may explain differences in fPSA analyses observed in archival serum.
The following articles in journals at HighWire Press have cited this article:
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  L. Zhu, H. Koistinen, U. Landegren, and U.-H. Stenman Proximity Ligation Measurement of the Complex between Prostate Specific Antigen and {alpha}1-Protease Inhibitor Clin. Chem., September 1, 2009; 55(9): 1665 - 1671. [Abstract] [Full Text] [PDF]
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 L. Bruun, C. Savage, A. M. Cronin, J. Hugosson, H. Lilja, and A. Christensson Increase in percent free prostate-specific antigen in men with chronic kidney disease Nephrol. Dial. Transplant., April 1, 2009; 24(4): 1238 - 1241. [Abstract] [Full Text] [PDF]
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 D. Ulmert, A. M. Serio, M. F. O'Brien, C. Becker, J. A. Eastham, P. T. Scardino, T. Bjork, G. Berglund, A. J. Vickers, and H. Lilja Long-Term Prediction of Prostate Cancer: Prostate-Specific Antigen (PSA) Velocity Is Predictive but Does Not Improve the Predictive Accuracy of a Single PSA Measurement 15 Years or More Before Cancer Diagnosis in a Large, Representative, Unscreened Population J. Clin. Oncol., February 20, 2008; 26(6): 835 - 841. [Abstract] [Full Text] [PDF]
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H. Lilja, D. Ulmert, T. Bjork, C. Becker, A. M. Serio, J.-A. Nilsson, P.-A. Abrahamsson, A. J. Vickers, and G. Berglund Long-Term Prediction of Prostate Cancer Up to 25 Years Before Diagnosis of Prostate Cancer Using Prostate Kallikreins Measured at Age 44 to 50 Years J. Clin. Oncol., February 1, 2007; 25(4): 431 - 436. [Abstract] [Full Text] [PDF]
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T. Steuber, A. J. Vickers, A. M. Serio, V. Vaisanen, A. Haese, K. Pettersson, J. A. Eastham, P. T. Scardino, H. Huland, and H. Lilja Comparison of Free and Total Forms of Serum Human Kallikrein 2 and Prostate-Specific Antigen for Prediction of Locally Advanced and Recurrent Prostate Cancer Clin. Chem., February 1, 2007; 53(2): 233 - 240. [Abstract] [Full Text] [PDF]
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