Percent free prostate-specific antigen in assessing the probability of prostate cancer under optimal analytical conditions

Although general consensus exists that percent free prostate-specific antig en (PSA) is superior to total immunoreactive PSA for prostate cancer (CaP) detection, its diagnostic performance is not yet well established. Analytic al problems may account for difficulties in evaluating percent free PSA bec ause the free PSA concentration is substantially lower than that of total P SA. The aim of the present study was to establish the diagnostic performanc es of the IMMULITE percent free PSA assay from Diagnostics Products Corp. u nder experimental conditions optimized to minimize analytical variability. Eighty-five patients with untreated primary CaP and 261 with untreated beni gn prostate hypertrophy (BPH) were prospectively enrolled. The Diagnostics Products IMMULITE total (Third Generation) and free PSA were measured by th e same technician, using the same instrument and the same reagent batch, We calculated the post-test probability to express how the likelihood of the diagnosis of CaP changed after the percent free PSA was determined, Areas u nder the ROC curves of percent free PSA were better than those of total PSA in every evaluated range of total PSA, The percent free PSA could have red uced the rate of unnecessary biopsies by 47% in patients with total PSA gre ater than or equal to 4 mu g/L with only 3.8% false-negative results. The p ost-test probability of percent free PSA was, however, <50% in men 50-70 ye ars of age, using cutoff points providing sensitivity from 99% to 80%, Perc ent free PSA is superior to total PSA in distinguishing primary CaP from BP H in patients with total PSA between 2 and 30 mu g/L, In men with low total PSA, the diagnostic performance of the percent free PSA assay may be optim ized by controlling methodological variability. The percent free PSA assay is effective in reducing the rate of unnecessary biopsies in men with total PSA >4 mu g/L. However, the post-test probability provided by percent free PSA is relatively low in asymptomatic patients 50-70 years of age.