A prostate specific antigen (PSA) test is one of the standard tests used for prostate cancer and other prostate diseases. PSA is a protein that is secreted by the cells of the prostate gland and is found in the semen, the medium that carries sperm.
Small amounts of PSA are also detectable in the blood, and PSA is considered to be at a healthy level if it is below 4 ng/ml. The chance of getting prostate cancer rises as the PSA level rises and this protein therefore acts as a biomarker for prostate cancer.
A PSA test is performed for two indications:
For the detection of prostate cancer
The PSA test may be performed as a diagnostic test in cases of suspected prostate cancer due to urinary symptoms, previous clinical or family history or the results of a physical examination.
For routine monitoring of prostate cancer
PSA is secreted in large amounts by prostate cancer cells. As the prostate cancer progresses, the blood levels of PSA rise and this marker can be used to provide clues about the growth or recurrence of a tumor after a patient has been treated.
PSA tests in men treated for prostate cancer
After treatment for prostate cancer with surgery, chemotherapy, radiation, hormonal therapy, biological therapy or any combination of these, the PSA levels should fall.
After a radical prostatectomy procedure, the blood PSA level should fall to an almost undetectable level (less than 0.1 ng/ml). After receiving treatment with radiotherapy, the level should also fall, although not as much as after surgery since the gland remains within the body and PSA is produced by both normal prostate cells and cancer cells. Ideally, the levels would fall to below 1.0 ng/ml, and at this level, the likelihood of cancer control is considered high.
If the PSA levels remain detectable or starts to increase after surgery, this is often a sign that cancer is persisting or recurring and repeat PSA tests are performed and the cancer monitored before the doctor decides on the next treatment approach.
If the PSA level continues to rise after radiotherapy, this again suggests that the cancer is returning. A steadily increasing PSA level is likely to lead to a recommendation of further treatment, usually in the form of hormonal therapy.
Reviewed by Sally Robertson, BSc