Ratio of free or complexed prostate-specific antigen (PSA) to total PSA: Which ratio improves differentiation between benign prostatic hyperplasia and prostate cancer?

Background: The aim of this study was to compare the diagnostic utility of a new assay that measures all forms of prostate-specific antigen complexed (cPSA) to serum proteins except alpha(2)-macroglobulin with the assay of fr ee PSA (fPSA) and the corresponding ratios to total PSA (tPSA) to improve t he differentiation between benign prostatic hyperplasia (BPH) and prostate cancer (PCa). Methods: Serum samples were collected from 91 men without prostate disease and with normal digital rectal examination (controls), 144 untreated patien ts with PCa, and 89 patients with BPH. tPSA and cPSA were measured using th e Bayer Immune 1 system; fPSA and the additional tPSA were measured with th e Roche Elecsys system. Results: The median cPSA/tPSA, fPSA/tPSA, and fFSA/cPSA ratios were signifi cantly different between patients with BPH and PCa (78.7% vs 90.7%, 25.5% v s 12.1%, and 36.8% vs 14.3%, respectively; P < 0.001). No correlations of c PSA and its ratios to tumor stage and grade were found. RC analysis showed that cPSA was not different from tPSA (areas under the curve, 0.632 vs 0.56 8), whereas the cPSA/tPSA ratio was similar to the fPSA/tPSA ratio in incre asing discrimination between BPH and PCa patients with tPSA concentrations in the tPSA gray zone between 2 and 10 mu g/L (areas under the curve, 0.851 vs 0.838). Conclusions: Compared with tPSA, the fPSA/tPSA and cPSA/tPSA ratios both im prove the differentiation between BPH and PCa comparably and are similarly effective in reducing the rate of unnecessary biopsies, whereas cPSA alone does not have any effect. (C) 2000 American Association for Clinical Chemistry.