New developments in the standardization of total prostate-specific antigen

Objective: Analytical evaluation of the calibration of three recently launc hed assays for the measurement of total prostate-specific antigen, i.e., IM x Total PSA (Abbott), Elecsys PSA (Roche), and IMMULITE 3rd Generation PSA (DPC). Design and methods: For accuracy assessment two reference materials were ap plied namely, Stanford 90:10 PSA Calibrator and Certified Reference Materia l 613 Prostate-Specific Antigen. Dilutions of these preparations were analy zed with all assays. In addition, clinical specimens from known prostate ca ncer or benign prostate hyperplasia patients and samples taken from an ongo ing prostate cancer screening study were used for comparison. Results: Application of the Stanford Calibrator revealed results well withi n 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 IMMULI TE results differed about 40% and the Elecsys about 18% from the calculated values. The comparison with clinical specimens showed statistically differ ent 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, S-y/x = 0.883 mu g/L) and y(Elecsys) = 0.98 x (IMMULI TE) + 0.38 (n = 97, r = 0.976, S-y/x = 0.733 mu g/L). In the lower measurin g range (PSA < 5.0 mu g/L) as measured with the screening samples (n = 43), these differences were less pronounced. Conclusion: In analytical sense a difference was found for both reference p reparations in the assays studied. Clinically, despite improvements in meth odology, results for total prostate-specific antigen are still not intercha ngeable. The possible consequences need to be elaborated. Copyright (C) 199 9 The Canadian Society of Clinical Chemists.