The free PSA is helpful in that patient with an elevated PSA but would rather not have a biopsy. The doctor and the patient agree to order it, a blood sample just like the regular PSA , but it is tested for the portion of PSA that is bound and unbound(free). If the free portion of the PSA is high, say greater than 25%, then the likelihood of the subsequent biopsy showing cancer is less than 5%. If the free is low, say less than 10%, then you might have a greater than 40% likelihood of a positive biopsy. So if you are inclined not to have the biopsy and your free PSA is very low, this information may persuade you to do the biopsy. This was the case for me, I was debating it myself, got a low free PSA, and went ahead with the biopsy.
Word of caution: I have had a patient with a very high free PSA and every core of the biopsy showed cancer. It’s a tool, not an absolute tool.
Also, I have noticed that the hits on this site have been high for the article on free PSA. I just now get it…. people are thinking that there is a link to being able to have their PSA drawn and run for free. That’s what it is.