[Usefulness of the percentage of free prostatic specific antigen in the differential diagnosis between benign prostatic hyperplasia and prostate cancer].

Background: PSA (prostatic specific antigen) is the most used tumor marker to monitor prostate cancer (PC). It is an acceptably sensitive test. Molecular forms of PSA give a chance to improve its specificity. We have evaluated the usefulness of the ratio free PSA/total PSA (f-PSA/t-PSA%) to diagnose prostate cancer, in the range between 4 and 20 ng/ml; i.e. the interval in which values overlap for patients with PC and benign prostatic hyperplasia (BPH) in our environment.
Patients and Methods: Prospective study on 269 patients, 73 with PC and 196 with BPH. Both t-PSA and f-PSA were determined using microparticles enzyme immune assay (MEIA) with AXSYM (Abbott) analyzer.
Results: Statistically significant differences were evidenced in f-PSA/t-PSA% for patients with PC vs. BPH; but that did not happen for t-PSA values. Sensitivity and specificity values were established for different cut-off points. ROC curve analysis proved diagnostic efficacy was better for f-PSA/t-PSA% than for t-PSA.
Conclusions: f-PSA/t-PSA percentage is a useful tool for the differential diagnosis between PC and BPH. A ratio lower than 12% selects a population with high risk of cancer. A percentage over 18% is useful to avoid or delay the indication of biopsy.