What it measures
PSA is a protein made by the prostate. Most PSA in the blood is bound to other proteins and a little circulates free. This ratio gives the free PSA as a percentage of total PSA.
Why people test it
- Added when total PSA is raised, to help judge whether further tests are needed.
- Used to help tell an enlarged prostate from prostate cancer, as the free share tends to differ.
- PSA is monitored on TRT, and the free share may be added if total PSA rises.
Typical range
Reported as a percentage and read alongside total PSA. Cut-offs vary by lab, method and age, and the report shows the lab's own.
Finger-prick or vein?
Offered as a vein draw only. Free PSA is less stable than total PSA once the blood is taken, so the sample needs to reach the lab promptly.
The NHS lists ejaculation and exercise that leaves you out of breath, including cycling, in the 48 hours before a PSA test as things that can raise the result.