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, biopsy might be recommended.
Why is Prostate Specific Antigen (Free) PSA done?
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
What does Prostate Specific Antigen (Free) PSA Measure?
The PSA (Free) Test measures the levels of unbound or free PSA in blood.
PSA is a protein which is secreted by the prostate gland. The prostate gland is a male accessory reproductive organ, the secretion of which contributes to the formation of the seminal fluid. Most of the PSA produced is secreted in the seminal fluid along with other prostatic secretions and only a small amount is secreted into the bloodstream. PSA is considered to be a tumor marker since its levels in the blood are elevated in prostate cancer and BPH, and it is used as a preliminary screening test before further diagnostic procedures.
PSA in blood is found as either complexed PSA (bound to other proteins) or free PSA. The PSA Test usually calculates the total PSA levels in the blood including both free and complexed forms, whereas the PSA (Free) test measures the levels of unbound or free PSA in blood.
Some doctors prefer to measure free PSA in patients with a total PSA level between 4 ng/ml and 10 ng/ml rather than subjecting everyone with an elevated PSA to a biopsy as it is an invasive procedure.
Interpreting Prostate Specific Antigen (Free) PSA results
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
Greater than 25%
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.