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Objectives: Prostate-specific antigen (PSA) is the most useful of all tumor markers. Although the sensitivity is impressive, low specificity results in a lack of cancer detection in a significant proportion of patients undergoing prostate biopsy. Several recent studies have addressed the need for improved specificity. Of all these approaches, the free/total PSA ratio appears to be the most promising. Given that most circulating PSA is complexed to alpha1-antichymotrypsin, and that this moiety represents a greater proportion of the total PSA in those men with carcinoma, we set out to determine whether complexed PSA would improve specificity in the detection of men with prostate cancer., Methods: Archival sera were obtained from 300 men, 75 of whom had biopsy-proved prostate cancer. All sera had been previously stored at -70 degrees C for variable periods. An investigative assay for complexed PSA (Bayer) was used. The Tandem-R free and total PSA assays (Hybritech) were used according to the manufacturer's recommendations., Results: Among all patients, specificities for the total PSA, free/total PSA, and complexed PSA alone were 21.8%, 15.6%, and 26.7%, respectively, at cutoffs yielding 95% sensitivity. Similar equivalence or superior performance, in terms of specificity relative to the free/total PSA ratio, was seen at other sensitivity thresholds and other total PSA ranges., Conclusions: Complexed PSA alone performs better than total PSA or the free/total PSA ratio and obviates the need for a second analyte determination. We believe this marker may offer significant enhancement in PSA testing with significant economic advantages.

Background: Consistency in prostate-specific antigen (PSA) quantitation by different PSA test manufacturers would minimize potential clinical confusion. The Ciba Corning ACS PSA2 calibration has been adjusted for alignment with a proposed international standard and clinical concordance with the Hybritech Tandem R assay. Herein we evaluate the clinical effectiveness of this recalibrated PSA test by comparing it with the IMx (Abbott Laboratories) and Tandem R (Hybritech) assays., Methods: Archival serum was used that had been stored at -70 degrees C from men who underwent ultrasound-guided prostate needle biopsy. Assays were run according to each manufacturer's specifications in singlicate on a single thaw., Results: The study included sera of 191 patients; 44 of the patients had carcinoma. There were 151 men with PSA (Tandem R) in the range of 0-10.0 ng/ml, 28 of whom had cancer. The correlation coefficients for Tandem R versus ACS, Tandem R versus IMx, and ACS versus IMx were 0.958, 0.955, 0.979 for benign patients and 0.960, 0.954, and 0.985 for those with cancer, respectively. The corresponding slopes were 1.029, 0.855, and 0.824 for men without and 1.044, 0.830, and 0.790, respectively, for those with malignancy., Conclusions: These data demonstrate substantial equivalence of the restandardized ACS assay and of the Hybritech method. Significant bias exists between these methods and the IMx assay with lower results being identified with the latter. These findings have significant implication, particularly in screening when results of an IMx assay are compared to other assays.