PSA free/total ratio

Free PSA divided by total PSA, usually printed as a percentage.

When the total is borderline, this is what helps separate benign prostate enlargement from something that needs investigating -- a higher ratio points toward the benign explanation.

It is only meaningful when the total sits in that borderline band; outside it the ratio adds nothing. Because it depends on the fragile free fraction, a sample that sat too long before processing reads falsely low.

Worth discussing together with the total PSA and its trend.