You’ve got the info you need, you just have the words jumbled up. You are asking about the percent (or ratio) of free PSA in total PSA, and you already have your answer: 24%.
A standard PSA tests measures total PSA, but as you probably know, PSA can be high for both cancerous and non-cancerous causes…in other words, the PSA test is not very “specific” for prostate cancer. We talked in a separate thread about how the PCA3 test can help determine whether someone with a moderately high PSA should go forward with a “uncomfortable” and costly biopsy. The measure of free PSA percentage serves a similar purpose…to indicate whether a biopsy is warranted.
Total PSA is made up of two sub-types: “free” and “bound” (or “complexed”) PSA. PSA gets “bound” to proteins when PC is present. Therefore, a low free PSA percentage suggests malignancy. The percent free PSA is a refinement of the PSA test, but once again (like the PCA3 test) there is a wide “gray zone” which between the high and low results.
Dr William Catalona, who is recognized as the developer of the PSA screening test (and a practicing prostate surgeon in Chicago) reported these stats:
If the percentage of free PSA is higher than 25%, the likelihood of prostate cancer is about 8%.
If the percentage of free PSA is less than 10%, then the likelihood of prostate cancer rises to 56%.
At 24%, you are on the favorable side of the “gray zone", although I wish that your PCA3 result was better. Keep in mind that both of these (PCA3 and % free PSA) are simply indicators whether you should have a biopsy. Someone does not definitively have PC until they get a biopsy result that says they do.
Good luck with your biopsy next week.