Prostate-Specific Antigen (PSA)
PSA stands for prostate-specific antigen. It is a protein that is created in the prostate tissue and is an enzyme that frees the sperm from the semen after ejaculation.
During the mid 80’s, the FDA approved its use to monitor the progress of prostate cancer that was already diagnosed and then in the mid 90’s the FDA approved the use of PSA as a means of prostate cancer screening along with a digital rectal examination.
Previous guidelines recommended that men over 50 years of age should have a PSA performed annually. Men who have a family history of prostate cancer and/or of African American descent was urged to have their PSA tested at the age of 40.
However, due to potential risks raised by some organization regarding the harm vs the benefits of early prostate cancer screening, such recommendations have shifted on the need to individual counseling of any man who maybe having his PSA check on the risk and benefits of test along with the potential need for a biopsy.
Of note, the need of routine PSA screening has been recommended in men actively receiving testosterone replacement therapy.
The range of Prostate-Specific Antigen can vary based on numerous conditions such as:
- Age of the individual
- Size of the prostate gland
- Presence of inflammation in the prostate
- Presence of a urinary tract infection
- Presence of prostate cancer
- Influence of medication such as testosterone, finasteride, dutasteride
- Recent sexual activity
- Recent prostate examination
- Indirect pressure on the perineum such as from riding a bike
Prostate- Specific Antigen Testing
In general, the consensus is that a consistent PSA reading below 4.0 ng/ml along with an absence of significant rise over a short period of time (0.75 ng/ml change in 12 month period) is at low risk of having prostate cancer.
Another common PSA test that is often ordered is a free PSA. This study measures the amount of PSA protein that is not bound to protein. When the ratio of free PSA relative to the total PSA is less than 25%, the greater the presence of prostate cancer. In general, the free PSA test is most appropriate when the total PSA is between 4 and 10 ng/ml.
Other techniques that have been used to gauge the importance of PSA include:
- PSA Density – Total PSA level divided by the volume of transition zone measurement of the prostate
- Age-specific PSA – Comparing the PSA relative to the individual age
- PSA velocity – Monitoring the elevation of PSA over time
More recently, newer forms of biomarker tests have become available to help determine the indication of a prostate biopsy.
- PCA3 – evaluate the level of a specific RNA strand in urine sample after a vigorous prostate massage.
- Prostate Health Index (PHI) – applies a sophisticated algorithm that measures the presence of total and free PSA as well as proPSA (a precursor form of free PSA) from a blood sample.
- Four-Kallikrein Panel (4Kscore) – compares the ratio total, free, and intact PSA as well as the presence of human kallikrein-2 (hK2) to determine the risk of detecting an aggressive form of prostate cancer.
