Discordant prostate specific antigen test results despite WHO assay standardization

Total PSA (tPSA) and free PSA (fPSA) are the most commonly used biomarkers for early detection of prostate cancer. Despite standardization efforts, many available PSA assays may still produce discordant results. In the present study, we compared four PSA assays calibrated to the WHO standards 96/670 and 96/668 for tPSA and fPSA, respectively.

Within the scope of the Prostate Cancer Early Detection Study Based on a ''Baseline'' PSA Value in Young Men (PROBASE), we tested tPSA and fPSA in serum samples from 50 patients in the four different PROBASE sites using four WHO-calibrated assays from Roche (Elecsys, Cobas), Beckman-Coulter (Access-II) and Siemens (ADVIA Centaur). The comparison was performed using the Passing-Bablok regression method.

Compared to Access, the median tPSA levels for Centaur, Elecsys, and Cobas were +3%, +11%-20%, and +17%-23%, respectively, while for median fPSA levels the differences for Centaur, Elecsys, and Cobas were +49%, +29%-31%, and +22%, respectively.

Despite all investigated assays being WHO-calibrated, the Elecsys and Cobas tPSA assays produced considerably higher results than the Access and Centaur assays. Differences in fPSA-recovery between all investigated assays were even more pronounced. When applying the tPSA cutoff of 3.1 μg/L recommended for WHO-calibrated assays, the use of higher calibrated assays may lead to unnecessary prostate biopsies. Conversely, if the historical threshold of 4 μg/L is applied when using WHO-calibrated assays, it could lead to falsely omitted prostate biopsies.

The International journal of biological markers. 2018 May 01 [Epub ahead of print]

Martin Boegemann, Christian Arsov, Boris Hadaschik, Kathleen Herkommer, Florian Imkamp, Jerzy-Roch Nofer, Joachim Gerß, Peter Albers, Axel Semjonow

1 Department of Urology, Prostate Center, University Hospital Münster, Muenster, Germany., 2 Department of Urology, Dusseldorf University Medical Center, Dusseldorf, Germany., 3 Department of Urology, University Hospital Essen, Essen, Germany., 4 Department of Urology, Technical University of Munich Klinikum rechts der Isar, Munich, Germany., 5 Department of Urology, Hannover University Medical Center, Hannover, Germany., 6 Center for Laboratory Medicine, University Hospital Muenster, Muenster, Germany., 7 Institute of Biostatistics and Clinical Research of the Westfalian Wilhelms-University Muenster, Muenster, Germany.