COMPARISON OF PROSTATE-SPECIFIC ANTIGEN (PSA) MEASURED BY 4 COMBINATIONS OF FREE PSA AND TOTAL PSA ASSAYS

We compared prostate-specific antigen (PSA) assay systems [i.e., free PSA (f-PSA) and the corresponding total PSA (t-PSA) assay] from four d ifferent manufacturers as well as the f-PSA/t-PSA ratios with regard t o their ability to discriminate between benign prostate hyperplasia (B PH) and prostate cancer (PCA), ROC analysis showed similar areas under the curves (AUCs) with different assay systems. For the entire patien t population the AUCs of the f-PSA/t-PSA ratio were not or slightly in creased compared with the sole measurement of t-PSA (t-PSA, 0.792-0.82 0; f-PSA/t-PSA ratio, 0.685-0.859). In contrast, for only those patien ts who showed t-PSA concentrations within the diagnostic gray area of 4-25 mu g/L t-PSA, the AUCs were greater for the f-PSA/t-PSA ratio tha n for measurement of t-PSA alone (t-PSA, 0.608-0.647; f-PSA/t-PSA rati o, 0.690-0.806). These results were confirmed by the predictive values of the negative results (NPVs) of the t-PSA assays and the f-PSA/t-PS A ratios (assay thresholds corresponding to a 95% detection limit). Co mpared with the sole t-PSA measurement there was no mentionable increa se in the NPVs due to the f-PSA/t-PSA ratio for the entire patient pop ulation, but an increase up to 49% when limited to t-PSA concentration s within 4-25 mu g/L. We therefore conclude that the f-PSA/t-PSA ratio may be helpful for differential diagnosis of BPH and PCA within the d iagnostic gray area of 4-25 mu g/L t-PSA.