Explain "free" PSA

ob66 Member Posts: 227 Member
I had a friend call me last night, knowing that I had been through the treatment of PCa over the last two years. He assumed I knew a lot on the subject because we have discussed my "study" a number of times. He went to his doctor and had a "free PSA" test and the result came out 10. I had not heard about free PSA and could be no help. Obviously I googled it immediately, after hanging up the phone, and got an answer that was "grey", especially with his numbers. They indicate if you have a high free PSA (opposite of what I was accustomed to) you were more likely involved with benign hyperplasia (above 15). If you are below 15 you should have further diagnosis, and if you are below 7 you probably have prostate cancer (on the last two numbers I may a bit hazy, and this is what is critical). Sounds like it is a test to determine whether biopsy is advisable. He is 75 years old, very healthy otherwise, and seems to have come away from this believing that his number (10) indicates that further investigation is not needed. Also, nothing palpable with DRE. After the little bit of reading that I did, I am not so sure that I concur.

My question is: Have you had, dealt with, or studied "free PSA" testing, and what is your knowledge? Any help would be appreciated.


  • silverfox1
    silverfox1 Member Posts: 36
    Free PSA
    ob66, I was recently diag. with PC and my regular PSA was 4.4. The issue that was concerning for the Doc. was that my free PSA number was a 3. My doc explained to me that the lower the free PSA the more likely the chance of PC. I had my biopsy and it was positive for PC. Hope this helps, I am sure that you will get more responses to help answer your questions. Have you tried calling the American Cancer hot line? It is 1-800-ACS-2345 they are open 24/7 and was an excellent resource for me!
  • davidp46
    davidp46 Member Posts: 11
    Free PSA
    I only have a laymen's understanding. The "regular" PSA test measures "serum" PSA where the antigen is "bound" to a protein. There is also some PSA circulating in the system that is not bound -- so it is "free" (i.e. unbound). The free PSA test ("fPSA") measures both free and bound PSA. Then the amount of free PSA is divided by the total (free+bound) PSA so that the free PSA as a percentage of total PSA is known. If the percent of free PSA is high (e.g. 15% or higher), **AND** the serum PSA is between 4 and 10, is it more likely that elevated serum PSA is cause by BPH or something other than PCa. Where the free PSA is low, it is more likely that PCa is causing the elevated PSA. Note that when the elevated PSA is >10, the interpretation of the numbers is "cloudy". Note too that your "regular" (serum) PSA number will not always match the "total" PSA reported on the free PSA assay. One large study comparing different PSA assays found up to a 28% different between two different assay. For example, in my case when I had my first free PSA test, we also did the standard (Siemens Centaur) test. My standard test PSA was ~~33 while my fPSA test reported total PSA of ~~42.

    My lay opinion is that mixing the test types is not very useful when trying to track "doubling" or "velocity" and so on.

    Others may have a better, and more technical explanation.

    Take care.