Here's a plot of the Risk (probability) of getting prostate cancer versus the % Free PSA / Total PSA ratio, for three different ages: 55, 65 and 75 y.o..
Interestingly, the PCa risk decreases as the % Free PSA ratio increases.
All men who have their PSA measured should ask for the % Free PSA test, as well.
Good question!
Yes, they are similar concepts. Free testostorone (bioavailable T) is testosterone that is not bound to SHBG proteins. The same true for any hormone, such as T3 and T4 thyroid hormones. You can get free T3 and T4 measured, as well as total T3 and T4. The free hormones are readily available to quickly react with cells, whereas the bound hormones are not free to react quickly with cells. So, the free/bioavailable hormones are the most important ones to track.
Bob
PSA, PSA Free Relevance When PSA Is Low
No difference in SBRT vs conventionally fractionated radiation for intermediate risk patientsShould SBRT be THE preferred treatment for intermediate risk prostate cancer?
PSA tests--Total vs. Ultrasensitive after radical prostatectomy
SRT vs Intermittent ADT Post-RP PSA recurrence 
