Toward metrological traceability in the determination of prostate-specific antigen (PSA): calibrating Beckman Coulter Hybritech Access PSA assays to WHO standards compared with the traditional Hybritech standards

Carsten Stephan 1 , 1 , Anna-Maria Kahrs 2 , 2 , Silke Klotzek 3 , 3 , Janett Reiche 4 , 4 , Christian Müller 5 , 5 , Michael Lein 6 , 6 , Serdar Deger 7 , 7 , Kurt Miller 8 , 8 ,  and Klaus Jung 9 , 9
  • 1 Department of Urology, Charité-Universitätsmedizin Berlin, Berlin, Germany
  • 2 Department of Urology, Charité-Universitätsmedizin Berlin, Berlin, Germany
  • 3 Department of Urology, Charité-Universitätsmedizin Berlin, Berlin, Germany
  • 4 Institute of Laboratory Medicine and Pathobiochemistry, Charité-Universitätsmedizin Berlin, Berlin, Germany
  • 5 Institute of Laboratory Medicine and Pathobiochemistry, Charité-Universitätsmedizin Berlin, Berlin, Germany
  • 6 Department of Urology, Charité-Universitätsmedizin Berlin, Berlin, Germany and Berlin Institute for Urologic Research, Berlin, Germany
  • 7 Department of Urology, Charité-Universitätsmedizin Berlin, Berlin, Germany
  • 8 Department of Urology, Charité-Universitätsmedizin Berlin, Berlin, Germany
  • 9 Department of Urology, Charité-Universitätsmedizin Berlin, Berlin, Germany and Berlin Institute for Urologic Research, Berlin, Germany

Abstract

Background: The metrological traceability of prostate-specific antigen (PSA) assay calibration to WHO standards is desirable to potentially improve the comparability between PSA assays. A method comparison was performed between the traditionally standardized Beckman Coulter Hybritech Access PSA and free PSA (fPSA) assays and a new alternate calibration of assays aligned to the WHO standards 96/670 and 96/668, respectively.

Methods: Sera from 641 men with and without prostate cancer, various control materials and mixtures of different proportions of the WHO standards were measured with both assay calibrations.

Results: Excellent comparability between the corresponding assay calibrations was observed, with correlation coefficients of at least 0.996. The Passing-Bablok slopes were 0.747 for total PSA (tPSA), 0.776 for fPSA and 1.02 for the percentage ratio of fPSA to tPSA (%fPSA), while the corresponding percentages of the new WHO-aligned assay results related to the traditional assays were 76.2%, 77% and 102.2%. Receiver operating characteristics revealed no differences between the two PSA assay calibrations.

Conclusions: The WHO calibration yields results approximately 25% lower for tPSA and fPSA values when compared with the conventional Hybritech calibration. Using the WHO-aligned PSA assay, a tPSA cut-off of 3 μg/L should be considered in clinical practice, while %fPSA cut-offs could be retained.

Clin Chem Lab Med 2008;46:623–9.

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Clinical Chemistry and Laboratory Medicine ( CCLM) publishes articles on novel teaching and training methods applicable to laboratory medicine. CCLM welcomes contributions on the progress in fundamental and applied research and cutting-edge clinical laboratory medicine. It is one of the leading journals in the field, with an impact factor of over three. CCLM is the official journal of nine national clinical societies and associated with EFLM.

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