Free-to-Total PSA Ratio

free-to-total PSA as a percent =

= (free PSA in ng/mL) / (total PSA in ng/mL)

Interpretation:

• A total PSA < 4 ng/mL is not considered increased, but prostate carcinoma can be present at this level (about a quarter of the patients with prostate cancer may have this serum level).

• A total PSA 4-10 ng/mL is a borderline increase, which can be seen with either benign prostatic hyperplasia or carcinoma.

• A total PSA > 10 ng/mL is increased; this level tends to be associated with a carcinoma but can be seen with benign prostatic hyperplasia.

• The free-to-total PSA ratio considered significant in different studies varies depending on whether the goal was greater sensitivity or specificity; a ratio of < 10% is more specific for prostate carcinoma while a ratio < 20% is more sensitive.

• Some use a free-to-total PSA ratio of 15% or less as an indication for prostate needle biopsy, while others use 19% or less.

(Table V, page 522, Chen, 1996)

Limitations:

• The ability of free-to-total PSA to discriminate between carcinoma and benign hyperplasia is seen when the prostate volume is < 40 cc; in patients with larger prostates, the ratio was unreliable in distinguishing between the two conditions (Stephan, 1997).

• Both the free and total PSA levels can show fluctuations, resulting in variation in the ratio unrelated to significant pathology. (Nixon, 1997).

• Performance of free and total antigen levels by different methods can introduce variability.