The influence of prostate volume on the ratio of free to total prostate specific antigen in serum of patients with
prostate carcinoma and benign prostatic hyperplasia.

Stephan C, Lein M, Jung K, Schnorr D, Loening SA.
Cancer 1997, 79: 104-109.

The ratio of free to total PSA (f-PSA to t-PSA) may help to distinguish patients with prostate cancer from those
with BPH because f-PSA% is lower in patients with prostate cancer. However, this study shows that f-PSA%
increases with prostate size. F-PSA% as a diagnostic test was most sensitive and specific when used in prostates
of less than 40 ml. Above 40 ml in size, the test performed poorly and limits the use of this test.