What is a prostate-specific antigen (PSA)?
Prostate-specific antigen (PSA) is a protein produced by the prostate gland. Blood levels of PSA can be elevated in men with prostate cancer.
For this reason, measurement of PSA in the blood has been used as a screening test for prostate cancer. However, the PSA test was first developed only to monitor men who had a history of prostate cancer. Views about PSA screening and appropriate follow-up have been evolving.
What constitutes an elevated prostate-specific antigen (PSA)?
No single normal level has been established. Historically, a level of 4.0 ng/mL or higher was used to justify a biopsy of the prostate (a sample of prostate tissue) to try and determine if a man has prostate cancer. However, this practice has been changing and other factors are being considered in the decision to perform a prostate biopsy.
Also, the thinking with regard to the management of prostate cancer continues to evolve. Considerations include:
- Aggressiveness of the cancer.
- Volume of cancer detected on biopsy.
- How it will affect a man’s longevity (length of life).
Does a prostate-specific antigen (PSA) level higher than 4.0 mg/mL mean that I have prostate cancer? Can prostate cancer be ruled out if my level is less than 4.0 ng/mL?
No, prostate cancer has been detected in men with levels less than 4.0 ng/mL. And many men with PSA levels higher than 4.0 ng/mL do not have prostate cancer. There is no PSA level below which the risk of cancer is zero. Two men with the same PSA level may have very different risks of prostate cancer depending on other risk factors.
Factors other than prostate cancer can cause the PSA level to be higher. These include:
- An enlarged prostate and prostate inflammation (prostatitis).
- Urinary tract infection.
- Having had a urinary catheter placed.
Drugs known as 5-alpha reductase blockers (finasteride or dutasteride), which are used at times to treat an enlarged prostate, will lower PSA levels. These factors are important to consider when interpreting the PSA test result.
Generally, higher PSA levels are associated with higher risks of prostate cancer.