PSA Testing Conducted & Supported by The Graham Fulford Charitable Trust

Testing free and bound PSA



A standard PSA test

measures the total PSA in the blood. But PSA has different forms. It can either be

Bound – attached to a protein in the blood
Free – not attached to a protein

We know from research that the proportions of free and bound PSA are different in men with prostate cancer, compared to men who have benign prostate disease. The general opinion is that a higher amount of free PSA in a test means a lower chance of cancer. Many doctors think that if more than a quarter (25%) of the total PSA is free, there is less chance of having prostate cancer. Put another way, men with prostate cancer are thought to have a lower proportion of free PSA.

So it is possible this test could help doctors find the cause of a raised PSA level. This might mean that some men with benign conditions avoid unnecessary biopsies. But methods of testing free and bound PSA in laboratories vary. And doctors are not agreed on the ratios of free to bound PSA that indicate cancer. So it is not used routinely in diagnosing prostate cancer. You are more likely to have it done if your standard PSA test result was borderline.
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