title: Serum free prostate-specific antigen in the diagnosis of prostate cancer.
abstract: 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).
  
  
  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, 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 significantly associated with the f/tPSA ratio; the ratios did not vary significantly 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%, respectively; the corresponding values for a tPSA of > 4 ng/mL were 30% and 52%.
  
  
  CONCLUSIONS
  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.
authors.affiliation: University Urology Unit, Freeman Hospital, Newcastle upon Tyne, UK.
authors.forename: H Y
authors.initials: HY
authors.lastname: Leung
authors.forename: L C
authors.initials: LC
authors.lastname: Lai
authors.forename: J
authors.initials: J
authors.lastname: Day
authors.forename: J
authors.initials: J
authors.lastname: Thomson
authors.forename: D E
authors.initials: DE
authors.lastname: Neal
authors.forename: F C
authors.initials: FC
authors.lastname: Hamdy
mesh_terms: D001706:Biopsy; D015331:Cohort Studies; D006801:Humans; D008297:Male; D009363:Neoplasm Proteins / Q000097:blood*; D011237:Predictive Value of Tests; D011446:Prospective Studies; D017430:Prostate-Specific Antigen / Q000097:blood*; D011470:Prostatic Hyperplasia / Q000097:blood / Q000175:diagnosis*; D011471:Prostatic Neoplasms / Q000097:blood / Q000175:diagnosis*; D012680:Sensitivity and Specificity; D018084:Ultrasonography, Interventional
chemical_list: D009363:Neoplasm Proteins; D017430:Prostate-Specific Antigen