SERUM-FREE PROSTATE-SPECIFIC ANTIGEN IN THE DIAGNOSIS OF PROSTATE-CANCER

Objective To determine the value of the ratio of free prostate-specifi c antigen (fPSA) to total PSA (tPSA) in the diagnosis of benign prosta tic hyperplasia (BPH) and prostate cancer in a cohort of patients unde rgoing prostatic transrectal ultrasonography (TRUS), Patients and meth ods The study comprised 153 patients (99 with BPH and 54 with prostate cancer) undergoing diagnostic TRUS of the prostate. Patients with a t PSA of >30 ng/mL were excluded from analysis. Free PSA was assayed usi ng an immunoassay specific for unbound PSA (CanAg Diagnostics, Sweden) . Total PSA was measured using the HybriTech Tandem-R PSA immunoradiom etric assay in routine clinical use and this estimate was validated us ing the CanAg tPSA assay. Results The measurements of tPSA from both a ssay systems correlated closely. The f/tPSA ratios in patients with pr ostate cancer were significantly lower than in those with BPH (median values 0.152 and 0.2, respectively, P<0.01). In patients with prostate cancer, the median f/t PSA levels apparently declined with increasing tPSA levels but in those with BPH, the levels of tPSA were not signif icantly associated with the f/tPSA ratio; the ratios did not vary sign ificantly with age in either group, A f/tPSA ratio at a threshold of 0 .16 had positive and negative predictive values of 44% and 74%, respec tively; the corresponding values for a tPSA of >4 ng/ml, were 30% and 52%. Conclusion The f/tPSA ratio differs significantly between patient s with BPH and cancer but because there is a considerable overlap of f /tPSA ratios between the groups, f/tPSA values alone were not sufficie ntly specific to be used as a single diagnostic test.