In general, serum PSA levels increase due to physical changes to prostate architecture caused by trauma, infection, inflammation, prostate manipulation, benign prostatic hypertrophy (BPH) or malignancy. The sensitivity test levels to these changes serve as the basis for the clinical use of the test. The PSA concentration in the serum of healthy men is many fold lower than that in seminal fluid. PSA in seminal fluid is predominantly free or uncomplexed. In serum, the majority of PSA is bound to inhibitors such as antichymotrypsin and macroglobulin. Measured total PSA consists of free and bound PSA.
Medical scientists found that one in four patients with normal rectal exam and normal PSA levels between 4.0 and 10.0 ng/mL, already have prostate cancer. A Free-PSA determination may more likely indicate the presence or absence of prostate cancer. A cut-off point of 25% Free-PSA was established as demarkation line between a normal and abnormal result. Furthermore, it was found that 20% of men with benign disease as determined by biopsy and normal DRE (direct rectal examination) and a total PSA between 4 and 10 ng/mL presented with a Free-PSA value greater than 25%, i.e. normal.
Percent Free-PSA determination may establish relative risk of prostate cancer.
In order to perform the Free-PSA test, at the same time, a total PSA determination should be also done.
Values obtained with different assay methods should not be used interchangeably.