title: Determination of non-alpha1-antichymotrypsin-complexed prostate-specific antigen as an indirect measurement of free prostate-specific antigen: analytical performance and diagnostic accuracy.
abstract: BACKGROUND
  A new assay measures prostate-specific antigen (PSA) not complexed to alpha(1)-antichymotrypsin (nACT-PSA) after removing PSA complexed to ACT by use of anti-ACT antibodies. We evaluated nACT-PSA and its ratio to total PSA (tPSA) as alternatives to free PSA (fPSA) and its ratio to tPSA in differentiating prostate cancer (PCa) and benign prostatic hyperplasia (BPH) in patients with tPSA of 2-20 micro g/L.
  
  
  METHODS
  PSA in serum of 183 untreated patients with PCa and 132 patients with BPH was measured retrospectively on the chemiluminescence immunoassay analyzer LIAISON(R) (Byk-Sangtec Diagnostica) with the LIAISON tPSA and LIAISON fPSA assays. The nACT-PSA fraction was determined with a prototype assay measuring the residual PSA after precipitation of ACT-PSA with an ACT-precipitating reagent.
  
  
  RESULTS
  nACT-PSA was higher than fPSA in samples with fPSA concentrations <1 microg/L but lower in samples with >1 microg/L fPSA. The median ratios of fPSA/tPSA and of nACT-PSA/tPSA were significantly different between patients with BPH and PCa (19.4% vs 12.2% and 17.4% vs 13.0%, respectively). Within the tPSA ranges tested (2-20, 2-10, and 4-10 microg/L), areas under the ROC curves for the fPSA/tPSA ratios were significantly larger than those for nACT-PSA/tPSA. In the tPSA ranges <10 microg/L, the areas under the ROC curves for fPSA/tPSA were significantly larger than those for tPSA, whereas the areas for nACT-PSA/tPSA were not. At decision limits for 95% sensitivity and specificity, both ratios significantly increased specificity and sensitivity, respectively, compared with tPSA, but the fPSA/tPSA ratio showed higher values.
  
  
  CONCLUSIONS
  nACT-PSA and its ratio to tPSA provide lower diagnostic sensitivity and specificity than fPSA/tPSA. The fPSA/tPSA ratio represents the state-of-the-art method for differentiating between PCa and BPH.
authors.affiliation: Department of Urology, University Hospital Charité, Humboldt University, D-10098 Berlin, Germany.
authors.forename: Sebastian
authors.initials: S
authors.lastname: Wesseling
authors.forename: Carsten
authors.initials: C
authors.lastname: Stephan
authors.forename: Axel
authors.initials: A
authors.lastname: Semjonow
authors.forename: Michael
authors.initials: M
authors.lastname: Lein
authors.forename: Brigitte
authors.initials: B
authors.lastname: Brux
authors.forename: Pranav
authors.initials: P
authors.lastname: Sinha
authors.forename: Stefan A
authors.initials: SA
authors.lastname: Loening
authors.forename: Klaus
authors.initials: K
authors.lastname: Jung
mesh_terms: D000368:Aged; D001322:Autoanalysis; D006801:Humans; D007118:Immunoassay / Q000379:methods; D008163:Luminescent Measurements; D008297:Male; D008875:Middle Aged; D017430:Prostate-Specific Antigen / Q000097:blood*; D011470:Prostatic Hyperplasia / Q000175:diagnosis; D011471:Prostatic Neoplasms / Q000175:diagnosis; D011485:Protein Binding; D012372:ROC Curve; D012189:Retrospective Studies; D012680:Sensitivity and Specificity; D000514:alpha 1-Antichymotrypsin / Q000097:blood*
chemical_list: D000514:alpha 1-Antichymotrypsin; D017430:Prostate-Specific Antigen