TOTAL AND FREE PSA - A METHODICAL AND CLINICAL-EVALUATION OF 5 ASSAYS

We studied the methodical and clinical relevance of five determination assays for free PSA (f-PSA) in addition to the corresponding total PS A antigen (t-PSA). Methods: Both the total PSA- and free-PSA-values of frozen sera obtained pretherapeutically from 80 patients with carcino ma (PC) and 171 patients with benign hyperplasia of the prostate (BPH) were analysed by means of Enzymun-Test PSA/BM, PSA-RIACT/CIS, CanAg P SA EIA/Dia, Tandem-E PSA/Hyb, PSA IRMA/IBL and Enzymun-Test PSA free/B M, F PSA-RIACT/CIS, CanAg Anti Free PSA/Dia, Tandem-R free PSA/Hyb, FR EE PSA IRMA/IBL. Results: The coefficient of correlation between Hybri tech PSA assay and the other assays was determined in patients with be nign and malignant prostatic diseases. There was a strong overall corr elation with all assays measuring total or free PSA, respectively. A s atisfying correlation is also shown using a limited scale up to 50 ng/ mL for total PSA and 5 ng/mL for free PSA. At 95% specificity sensitiv ities of total PSA between 40% and 50% of the ratio (Q) = free PSA/tot al PSA between 4% and 28% were calculated In a second step only patien ts with total PSA values below the cutoff level of 16.5 [mu g/l] (BM), 13.9 [mu g/l] (CIS), 14.7 [mu g/l] (Dial, 15.7 [mu g/l] (Hyb) and 16. 8 [mu g/l] (IBL) were considered. Using the BM assays, of these patien ts 9 of 162 with BPH and 14 of 47 with PC [CIS: 14 of 162 with BPH and 4 of 48 with PC/Dia: 13 of 162 with BPH and 11 of 48 with PC/Hyb: 6 o f 156 with BPH (missing values=6) and 11 of 40 with PC/IBL: 11 of 160 with BPH (missing valnes=1) and 13 of 33 with PC (missing values=2)] w ere below the ratio Q=free PSA/total PSA. Considering both steps (feta l PSA and Q) using the BM assay 47 patients with PC were detected corr ectly and 18 patients with BPH would have been biopsied unnecessarily (positive biopsy rate=pos. br:: 72%) [CIS: 38 patients with PC and 23 patients with BPH (pos. br.: 62%)/Dia: 43 patients with PC and 22 pati ents with BPH (pos. br:: 66%)/Hyb: 51 patients with PC and 15 patients with BPH (pos. br.: 77%)/IBL: 46 patients with PC and 20 patients wit h BPH (pos. br.: 70%)] Conclusions: High total PSA levels of all assay s are a very good indicator for the presence of prostate cancer. There is still concern to improve the differentiation between BPH and PC, w hen an intermediate or low value (<95% specificity) is observed. The d etermination of Q is only useful in this range and it might be helpful for the clinicians decision to apply or avoid biopsy.