FACTORS INFLUENCING THE RATIO OF FREE TO TOTAL PROSTATE-SPECIFIC ANTIGEN IN SERUM

The ratio of free prostate-specific antigen (f-PSA) to total PSA (t-PS A) in serum, calculated as percent free PSA (f-PSA%), is lower in pati ents with prostate carcinoma (PCa) than in patients with benign prosta te hyperplasia (BPH). This parameter facilitates discrimination betwee n the 2 groups of patients, but there is an overlapping of data. A bet ter understanding of factors influencing this ratio is of practical im portance. Therefore, f-PSA% was measured in controls and patients suff ering from BPH, PCa and chronic prostatic inflammation with t-PSA conc entrations up to 20 mu g/l using the IMMULITE assays, The relationship s of f-PSA% to clinical situation, age, prostate volume, kind of treat ment, and stage and grade of tumor were calculated. Compared with cont rols or BPH patients, mean f-PSA% values were reduced in PCa patients and in patients with chronic prostatic inflammation, The prostate volu me was the most important factor to influence f-PSA%. The difference o f f-PSA% between PCa and BPH patients with prostate volumes smaller th an 40 cm(3) was lost if the prostate volumes exceeded 40 cm(3), No rel ationship of f-PSA% to pTNM stage or grade of tumor was observed, In c ontrast to t-PSA concentrations, the f-PSA% values were not age-depend ent and were not influenced by any kind of treatment in BPH and PCa pa tients 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%. (C) 1997 Wiley-Liss, Inc.