The ratio of free prostate‐specific antigen (f‐PSA) to total PSA (t‐PSA) in serum, calculated as percent free PSA (f‐PSA%), is lower in patients with prostate carcinoma (PCa) than in patients with benign prostate hyperplasia (BPH). This parameter facilitates discrimination between the 2 groups of patients, but there is an overlapping of data. A better understanding of factors influencing this ratio is of practical importance. Therefore, f‐PSA% was measured in controls and patients suffering from BPH, PCa and chronic prostatic inflammation with t‐PSA concentrations up to 20 μg/l using the IMMULITE assays. The relationships of f‐PSA% to clinical situation, age, prostate volume, kind of treatment, and stage and grade of tumor were calculated. Compared with controls or BPH patients, mean f‐PSA% values were reduced in PCa patients and in patients with chronic prostatic inflammation. The prostate volume was the most important factor to influence f‐PSA%. The difference of f‐PSA% between PCa and BPH patients with prostate volumes smaller than 40 cm3 was lost if the prostate volumes exceeded 40 cm3. No relationship of f‐PSA% to pTNM stage or grade of tumor was observed. In contrast to t‐PSA concentrations, the f‐PSA% values were not age‐dependent and were not influenced by any kind of treatment in BPH and PCa patients either, which simplifies the use of f‐PSA% compared with t‐PSA. Thus, for using f‐PSA% in clinical practice and for interpreting the data correctly, the advantages shown have to be considered along with the potential limitations of f‐PSA%. Int. J. Cancer 74:630–636.© 1997 Wiley‐Liss, Inc.

No abstract

Chronic prostatitis is not characterized by elevated total PSA concentrations alone but also by a decreased percentage of free PSA, a tendency similar to that in prostate cancer. This unspecific change in percentage of free PSA must be considered to interpret the percentage of free PSA correctly.