What is a free PSA level?
In the blood, PSA can circulate alone (free) or bound to other proteins (complexed). It is by measuring both the free and complexed forms of PSA that a total PSA, the number most commonly ordered as a first test, is determined. In men with an elevated or concerning PSA level, breaking down the PSA into free and complexed forms can give more information about the risk of cancer. In all men, the majority of PSA circulates in the complexed form, but in men with prostate cancer, more PSA on average is complexed than in men without prostate cancer. As such, a lower free PSA, or a lower free-to-total PSA ratio, is more suggestive of cancer than a high free-to-total ratio. The free-to-total ratio is the most common method by which free PSA is reported. It is generally felt that a ratio of greater than 25% is reassuring, 15-25% is suspicious and below 15% is very suspicious for cancer. Smilow Center physicians have been active in evaluating free and complexed PSA in their prediction of prostat
