PSA, Free
The portion of PSA that circulates unbound to proteins.
What it measures
Most PSA in blood is bound to protease inhibitors; a smaller fraction circulates free. Benign prostate enlargement tends to produce relatively more free PSA than cancer does.
Why it matters
Free PSA is mainly used to calculate the percent free PSA, which helps estimate prostate cancer probability when total PSA is moderately elevated.
What a high result can mean
Higher free PSA, relative to total PSA, is more typical of benign prostatic hyperplasia.
What a low result can mean
Lower free PSA relative to total PSA is associated with a higher likelihood of prostate cancer.
What affects the result
Has no standalone reference range; interpret as percent free PSA. Same pre-test precautions as total PSA.
Units and conversion
Usually reported in ng/mL.
- From ug/L: multiply by 1 to get ng/mL
Also called on lab reports
Free PSA, PSA Free, Prostate Specific Antigen, Free, Free Prostate Specific Antigen
Related tests: Prostate
This page is educational and does not replace advice from a healthcare professional.