On the standardization of total prostate-specific antigen: an exercise with two reference preparations

In this study, 112 serum samples were analyzed for total prostate-specific antigen with three well-established assays i.e. Tandem R and Tandem E (both from Hybritech Inc., San Diego, USA) and Prostatus Free/Total from Wallac Oy, Turku, Finland. Thirty-two samples were collected from prostate cancer patients, 32 from patients with benign prostate hyperplasia and 48 from men participating in a screening study for prostate cancer. The aim of the study was to compare the results before and after recalculat ion with the data obtained with two reference preparations for total prosta te-specific antigen: Stanford 90:10 PSA Calibrator and Certified Reference Material 613 Prostate-Specific Antigen. Comparing the actual results revealed almost perfect correlations between T andem R and Tandem E and between both Tandem assays and Prostatus. We obser ved statistically significant differences in accuracy between Tandem R and Tandem E: y(Tandem E) = 1.05 x (Tandem R) + 0.07 and between Tandem E and Prostatus: y(Prostatus) = 0.94 x (Tandem E) + 0.02 In both comparisons prostate-specific antigen values ranged from 0-40 mu g/ l. Recalculation with both reference preparations did not solve these discrepa ncies. One exception was the combination Tandem R and Tandem E. The applica tion of either reference preparation solved the differences in accuracy her e. In conclusion, even after recalibration, assays for total prostate-specific antigen are still not completely interchangeable.