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.
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 microg/L should be considered in clinical practice, while %fPSA cut-offs could be retained.
Department of Urology, Charité - Universitätsmedizin Berlin, Berlin, Germany.
Carsten
C
Stephan
Anna-Maria
AM
Kahrs
Silke
S
Klotzek
Janett
J
Reiche
Christian
C
Müller
Michael
M
Lein
Serdar
S
Deger
Kurt
K
Miller
Klaus
K
Jung
D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D002138:Calibration; D002624:Chemistry, Clinical / Q000295:instrumentation / Q000379:methods / Q000592:standards*; D006801:Humans; D008297:Male; D008875:Middle Aged; D017430:Prostate-Specific Antigen / Q000097:blood*; D011471:Prostatic Neoplasms / Q000097:blood* / Q000175:diagnosis*; D012015:Reference Standards; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D014944:World Health Organization
D017430:Prostate-Specific Antigen