New developments in the standardization of total prostate-specific antigen.
OBJECTIVE
Analytical evaluation of the calibration of three recently launched assays for the measurement of total prostate-specific antigen, i.e., IMx Total PSA (Abbott), Elecsys PSA (Roche), and IMMULITE 3rd Generation PSA (DPC).


METHODS
For accuracy assessment two reference materials were applied namely, Stanford 90:10 PSA Calibrator and Certified Reference Material 613 Prostate-Specific Antigen. Dilutions of these preparations were analyzed with all assays. In addition, clinical specimens from known prostate cancer or benign prostate hyperplasia patients and samples taken from an ongoing prostate cancer screening study were used for comparison.


RESULTS
Application of the Stanford Calibrator revealed results well within 10% of the calculated values for all assays. Regarding the CRM Calibrator only the IMx Total PSA proved to approach the line of identity. The IMMULITE results differed about 40% and the Elecsys about 18% from the calculated values. The comparison with clinical specimens showed statistically different results for the combination IMMULITE-IMx and for IMMULITE-Elecsys. The regression lines for both collections were: y(IMx) = 0.86x(IMMULITE) +0.12 (n = 104, r = 0.970, Sy/x = 0.883 microg/L) and y(Elecsys) = 0.98x(IMMULITE) +0.38 (n = 97, r = 0.976, Sy/x = 0.733 microg/L). In the lower measuring range (PSA <5.0 microg/L) as measured with the screening samples (n = 43), these differences were less pronounced.


CONCLUSIONS
In analytical sense a difference was found for both reference preparations in the assays studied. Clinically, despite improvements in methodology, results for total prostate-specific antigen are still not interchangeable. The possible consequences need to be elaborated.
Blijenberg
B G
BG
Department of Clinical Chemistry, University Hospital Rotterdam, The Netherlands. blijenberg@ckcl.azr.nl
Storm
B N
BN
Van Zelst
B D
BD
Kruger
A E
AE
Schröder
F H
FH
D002138:Calibration; D006801:Humans; D007118:Immunoassay / Q000379:methods; D008297:Male; D017430:Prostate-Specific Antigen / Q000032:analysis / Q000097:blood*; D011470:Prostatic Hyperplasia / Q000097:blood / Q000175:diagnosis*; D011471:Prostatic Neoplasms / Q000097:blood / Q000175:diagnosis*; D011933:Reagent Kits, Diagnostic; D012044:Regression Analysis; D015203:Reproducibility of Results; D012661:Semen / Q000737:chemistry
D011933:Reagent Kits, Diagnostic; D017430:Prostate-Specific Antigen