We studied the methodical and clinical relevance of five determination assays 
for free PSA (f-PSA) in addition to the corresponding total PSA antigen (t-PSA).
METHODS: Both the total PSA- and free-PSA-values of frozen sera obtained 
pretherapeutically from 80 patients with carcinoma (PC) and 171 patients with 
benign hyperplasia of the prostate (BPH) were analysed by means of Enzymun-Test 
PSA/BM, PSA-RIACT/ CIS, CanAg PSA EIA/ Dia, Tandem-E PSA/Hyb, PSA IRMA/ IBL and 
Enzymun-Test PSA free/BM, F PSA-RIACT/CIS, CanAg Anti Free PSA/Dia, Tandem-R 
free PSA/Hyb, FREE PSA IRMA/IBL.
RESULTS: The coefficient of correlation between Hybritech PSA assay and the 
other assays was determined in patients with benign and malignant prostatic 
diseases. There was a strong overall correlation with all assays measuring total 
or free PSA, respectively. A satisfying 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 sensitivities of total PSA between 40% and 50% of the ratio (Q) = 
free PSA/total PSA between 4% and 28% were calculated. In a second step only 
patients with total PSA values below the cutoff level of 16.5 [micrograms/l] 
(BM), 13.9 [micrograms/l] (CIS), 14.7 [micrograms/l] (Dia), 15.7 [micrograms/l] 
(Hyb) and 16.8 [micrograms/l] (IBL) were considered. Using the BM assays, of 
these patients 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 of 156 
with BPH (missing values = 6) and 11 of 40 with PC/IBL: 11 of 160 with BPH 
(missing values = 1) and 13 of 33 with PC (missing values = 2)] were below the 
ratio Q = free PSA/total PSA. Considering both steps (total PSA and Q) using the 
BM assay 47 patlents with PC were detected correctly 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 patients 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 with BPH (pos. br.: 70%)]
CONCLUSIONS: High total PSA levels of all assays are a very good indicator for 
the presence of prostate cancer. There is still concern to improve the 
differentiation between BPH and PC, when an intermediate or low value (< 95% 
specificity) is observed. The determination of Q is only useful in this range 
and it might be helpful for the clinicians decision to apply or avoid biopsy.