This study examined the clinical relevance of the determination of free PSA 
(f-PSA) in addition to total PSA (t-PSA) in 6 study groups.
PATIENTS AND METHODS: Both total PSA- and free PSA-values of sera samples 
obtained pretherapeutically from 455 patients with carcinoma (PCA) and 680 
patients with benign hyperplasia of the prostate (BPH) were analyzed by means of 
Enzymun-Test PSA and Enzymun-Test Free PSA (Boehringer Mannheim GmbH, Germany).
RESULTS: At 95% specificity (true negative test results), a cutoff value of 13.6 
[micrograms/L] was obtained for total PSA (34 patients with BPH [5%] were above 
this value). For this cutoff value we calculated a sensitivity (true positive 
test results) of 44%. Using the same criteria for the ratio Q = f-PSA:t-PSA a 
cutoff of 0.13 was found again at a specificity of 95%. In a second step only 
patients with total PSA values below the cutoff level of 13.6 [micrograms/L]) 
were considered. Out of these patients 26 of 646 with BPH and 108 of 257 with 
PCA were below the above mentioned ratio (Q = 0.13). Considering both steps 
(total PSA and Q) 306 patients with PCA were detected correctly and 60 patients 
with BPH would have been biopsied unnecessarily.
CONCLUSION: High total PSA levels are a very good indicator for the presence of 
prostate cancer. There is still concern to improve the differentiation of the 
diagnosis between BPH and PCA, when an intermediate or low value (< or = 95% 
specificity) is observed. The determination of the ratio is only useful in this 
range. It is more powerful at discriminating between PCA and BPH than t-PSA 
alone and may contribute to a reduction in unnecessary invasive techniques.