Serum free prostate‐specific antigen in the diagnosis of prostate cancer

Objective To determine the value of the ratio of free prostate‐specific antigen (fPSA) to total PSA (tPSA) in the diagnosis of benign prostatic hyperplasia (BPH) and prostate cancer in a cohort of patients undergoing prostatic transrectal ultrasonography (TRUS). Patients and methods The study comprised 153 patients (99 with BPH and 54 with prostate cancer) undergoing diagnostic TRUS of the prostate. Patients with a tPSA of >30 ng/mL were excluded from analysis. Free PSA was assayed using an immunoassay specific for unbound PSA (CanAg Diagnostics, Sweden). Total PSA was measured using the HybriTech Tandem‐R PSA immunoradiometric assay in routine clinical use and this estimate was validated using the CanAg tPSA assay. Results The measurements of tPSA from both assay systems correlated closely. The f/tPSA ratios in patients with prostate cancer were significantly lower than in those with BPH (median values 0.152 and 0.2, respectively, P4 ng/mL were 30% and 52%. Conclusion The f/tPSA ratio differs significantly between patients with BPH and cancer but because there is a considerable overlap of f/tPSA ratios between the groups, f/tPSA values alone were not sufficiently specific to be used as a single diagnostic test.