This study examined the clinical relevance of the determination of free PSA (f-PSA) in addition to total PSA (t-PSA).
Patients and methods: Both 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 PSA IRMA and FREE PSA IRMA (IMMUNOCORP/IBL).
Results: At 95% specificity (true negative test results), a cut-off value of 16.8 [micrograms/L] was obtained for total PSA (9 patients with BPH [5%] were above this value). For this cut-off value we calculated a sensitivity (true positive test results) of 41%. Using the same criteria for the ratio Q = f-PSA:t-PSA a cut-off of 0.083 was found again at a specificity of 95%. In a second step only patients with total PSA values below the cut-off level of 16.8 [micrograms/L]) were considered. Of these patients 11 of 160 with BPH (missing values = 1) and 13 of 33 with PC (missing values = 2) were below the above mentioned ratio (Q = 0.083). Considering both steps (total PSA and Q) 46 patients with PC were detected correctly and 20 patients with BPH would have been biopsied unnecessarily (positive biopsy rate: 70%).
Conclusion: High total PSA levels are a very good indicator for the presence of prostate cancer. There is still concern to improve the differentiation between the diagnosis between BPH and PC, when an intermediate or low value (< or = 95% specificity) is observed. The determination of Q is only useful in this range and might be helpful for the clinician's decision to apply or avoid biopsy.