Hi Larry...I think many (most?) of the men here have had their free PSA
measured as they progress through diagnosis to treatment.  The topic is
routinely brought up and discussed in posts to the newly diagnosed.
The literature suggests that fPSA still has diagnostic meaning for men
with PSA >= 2.6, so the topic might not be discussed with men who have
lower PSA values.    So, fPSA is useful to men to help clarify
diagnosis, and also to men who are practicing WW and need to monitor
their disease progression (or, hopefully, lack thereof).  For men who
have undergone definitive treatment, such as RP and RT, a fPSA
measurement has no informational content and is a waste of money and
medical resource.  As far as people know today, fPSA is produced by
proteolysis (cleaving) of specific PSA bonds while the PSA molecule is
still contained within the prostate (specifically the lumens within the
prostate).  The altered form (fPSA) and normal form (PSA) both leak out
of the prostate.  The regular PSA is immediately complexed in the sera.
The ductal system that carries PSA to the lumens is disrupted in PCa,
so less fPSA is usually generated in men with PCa for this reason.
There are also other PSAs besides the "normal" and "free".  The normal
form is a protein with 237 amino acids, some of these amino acids
contain sulfur.  The sulfurs can bond (disulfide bridge) and cause
normal PSA to have a unique 3D structure.  Breaking these bonds leads
to fPSA.  Additionally there is prepro- and pro-PSA, both precursors to
PSA containing a few more amino acids.  The amounts of pro-PSA appears
to be different between men with normal and cancerous prostates.  Work
is ongoing to see if such markers might provide additional diagnostic
information and / or higher accuracy in deciding who needs a biopsy.
This is interesting stuff, but I should probably stop here...Best
wishes and good health, Ron

Larry, I didn't know you could have a freePSA with such a low "regular"
PSA. Can you expand on that, please. I'd like to get a freePSA (my PSA
is .8) but PCa runs in the family.