The prostate-specific antigen (PSA) test is commonly used to detect prostate cancer. Prostate-specific antigen (PSA) is a protein made in the prostate gland. PSA liquefies semen so sperm are better able to travel up the female reproductive tract.
When the prostate is healthy, very little PSA escapes into the bloodstream. Sometimes, due to diseases or an enlarged prostate gland, the walls between the prostate and the bloodstream may break down and allow more PSA into the blood. PSA can be detected by a blood test.
Abnormal levels of prostate-specific antigen often indicate that a man has prostate cancer. Testing for high PSA levels allows doctors to assess a man’s prostate cancer risk. Generally, when cancer is present, the higher the PSA level is, the larger the prostate cancer is and the more likely it is to have spread beyond the prostate.
However, the PSA levels alone do not provide enough information to distinguish between benign prostate conditions and cancer. PSA testing only serves as a screening means to indicate if a prostate problem exists. The doctor takes the PSA test results into account, along with other factors, before deciding if additional testing is required.
PSA is measured in terms of nanograms per milliliter, or ng/ml. A PSA of 4 to 10 ng/ml is considered slightly elevated, 10 to 20 is moderately elevated, and above 20 is highly elevated.
One high PSA reading does not necessarily require more tests. This is because certain factors can cause PSA levels to rise or fall. For example, bed rest may lead to a drop in PSA levels, while cycling may lead to a rise in PSA levels. Before having a PSA test, you may want to refrain from sexual activity for 1 to 2 days. If you have had a cystoscopy, schedule your PSA test only several weeks after your cystoscopy.
If your PSA level is slightly elevated, your doctor may choose to monitor your PSA levels to determine if they continue to rise over time. If levels continue to rise, he or she may suggest more extensive tests.
PSA test results alone is not sufficient to determine if a man has prostate cancer. Most men with abnormal PSA levels are not diagnosed with cancer. Only 25 to 30 percent of men with PSA levels higher than 4 ng/ml will be biopsied and diagnosed with cancer. 15 in 100 men over 50 will have elevated PSA levels but only 3 of these will have prostate cancer. Conversely, there are men with extremely low PSA levels who had biopsies showing cancer.
Because of this, doctors generally recommend the use of the digital rectal examination (DRE) as well as the PSA test to detect prostate cancer.