What is a Prostate Specific Antigen (PSA)?
PSA is an abbreviation for Prostate Specific Antigen. It is a protein produced by prostate tissue, both benign and cancerous. No other tissues produce PSA. It is released by prostate tissue into the blood stream and can be measured by a routine blood test.
How is the PSA Blood Test Used?
The PSA test serves three primary functions:
Prostate Cancer Screening: PSA (along with a digital rectal examination) is used as a test to screen for prostate cancer. An elevated PSA level (>2.5 ng/ml) is suggestive of prostate cancer, although there are other related reasons why the PSA may be elevated. These include benign enlargement of the prostate or a prostate infection. When a patient is diagnosed with prostate cancer their PSA test may be included in other exams.
Prognosis: Once prostate cancer is diagnosed, PSA is used as a prognostic factor. The degree of elevation generally correlates with the amount of cancer present. Men with early stage prostate cancer tend to have a low PSA (<10 ng/ml). Men with advanced prostate cancers tend to have a higher PSA. The higher the PSA, the greater the probability that the cancer has invaded through the capsule of the prostate, spread to the lymph nodes, or spread to other parts of the body.
Follow-up: Once prostate cancer is treated, PSA is used to monitor the success of the treatment. Following treatment, the PSA should be very low and stable. A rising PSA is generally indicative of a recurrence.
Prostate Cancer Risk Stratification
After a prostate cancer diagnosis the doctor needs to be able to estimate the likelihood of cancer spreading outside the prostate. The three factors used to determine the estimate include: cancer staging based on a rectal exam, Gleason Score, and the PSA which are described in greater detail below.