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What Is Free PSA?

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Last Modified: March 1, 2011

Dear OncoLink "Ask The Experts,"

What is the free PSA test and how does that differ from regular PSA test?

Neha Vapiwala , MD, Senior Editor of OncoLink and Chief Resident in the Department of Radiation Oncology at the Hospital of the University of Pennsylvania, responds:

So prostate specific antigen (PSA) circulates in the blood in two forms: free or attached to a protein molecule. The regular PSA test is a combo of the free and attached. The free PSA test is sometimes used for men who have higher total PSA values because it may help tell what kind of prostate problem a man has. With benign prostate conditions (like BPH), there is usually more free PSA, while cancer tends to produce more of the attached form. If a man’s attached PSA level is high but his free PSA level is not, the presence of cancer is more likely. In this case, more testing, such as a prostate biopsy, may be done. Ultimately, biopsy is always needed to confirm the actual diagnosis.

This question and answer was part of the OncoLink Brown Bag Chat Series. See the full transcript of Prostate cancer treatment: where are we now?