Prostate Specific Antigen (Free) PSA
Understanding Prostate Specific Antigen (Free) PSA
What is Prostate Specific Antigen (Free) PSA?
The Prostate-Specific Antigen (Free) Test measures the levels of unbound or free prostate-specific antigen (PSA) in blood. PSA in the blood is found as either complexed PSA (bound to other proteins) or free PSA. Free and total PSA tests can help diagnose prostate problems including prostate cancer. However, the results are only meaningful when compared with those of a total PSA test.
A higher ratio of free PSA to total PSA indicates a lower risk of prostate cancer. On the other hand, a low ratio of free PSA to total PSA indicates a higher risk of having prostate cancer. Free PSA tests are quicker, cheaper, and less invasive than biopsies, but they cannot confirm or rule out cancer. If the levels initially indicate a possible risk of prostate cancer, a biopsy might be recommended.
What is Prostate Specific Antigen (Free) PSA used for?
The PSA (Free) Test is performed:
· To identify the need for Prostate biopsy in patients with increased PSA (Total) levels
· To differentiate between Prostate cancer and other benign conditions of the Prostate gland like BPH
Interpreting Prostate Specific Antigen (Free) PSA results
Interpretations
The normal value of PSA (total) in blood is below 4.0 ng/ml
Total PSA levels roughly between 4.0 and 10.0 ng/ml are considered in “grey zone” and the probability of finding prostate cancer based on % free PSA in such cases is given below:
% free PSA |
Probability of prostate cancer |
0%–10% |
56% |
10%–15% |
28% |
15%–20% |
20% |
20%–25% |
16% |
Greater than 25% |
8% |
Some patients with a “normal” total PSA may have cancer. So, some doctors order both tests at the same time as a low total PSA and a low percentage of free PSA would probably indicates biopsy in these cases.