Prostate specific antigen (PSA) is a protein that is produced by cells in the prostate. The prostate is small gland around the urethra that produces fluid found in semen. Small parts of the fluid are released into the blood stream and the test measures this amount of PSA in the blood.
PSA is also known as a tumor marker and is used to screen and monitor for prostate cancer as high PSA levels are associated with prostate cancer. Other common causes of increased levels include infection (prostatitis) and enlargement (benign prostatic hyperplasia - BPH). PSA levels increase in all men over time.
The test is used for screening for cancer but cannot make the diagnosis. The gold standard test is to have a prostate biopsy done where tissue is microscopically analysed for cancerous cells. The PSA level in conjunction with a clinical examination and specifically a prostate examination will determine whether a biopsy needs to be done. Prostate cancer is common in males with the risk increasing with age. The cancer can progress very slowly and symptoms are often not present initially that is why annual screening of males over the age of 50 is recommended.
Clinicians may also request other tests when the PSA level is elevated to exclude other causes e.g. a urine analysis to look for infection and a prostate ultrasound.
Once the diagnosis of prostate cancer is made the PSA test may be used for monitoring to determine the response to treatment.
The PSA test is used to screen men for prostate cancer:
The PSA test can also be ordered when symptoms of possible prostate cancer are present including:
Once an elevated level is detected a healthcare practitioner may request a follow-up test in a few weeks to see if there was a change.
The PSA test may also be ordered at regular intervals during treatment for prostate cancer, in order to monitor the response to therapy as well as recurrence.