Prostate specific antigen testing

The prostate specific antigen or PSA test helps you and your doctor to assess your risk of having prostate cancer. It can also be used to help assess how successful treatment has been. In this section we will review only the use of the PSA test in the assessment of risk of having prostate cancer.

What is a PSA Test?

PSA or prostate specific antigen is a normal protein-based product made by the prostate and secreted into the semen; PSA may play a role in male fertility. Some of the PSA made by the prostate seems to “leak” into the bloodstream. Under normal circumstances, blood PSA levels are very low.

Prostate cancer can increase the amount of PSA that “leaks” into the bloodstream. This is why testing PSA in the blood can help detect prostate cancer.

When your doctor recommends a PSA test (s)he is referring to measurement of PSA levels in your blood. We are talking about a very simple test, one that can be combined with other blood tests, such as your cholesterol test. To do it, someone will take a blood sample and send it to a laboratory for testing.

The higher your PSA level, the higher the likelihood that you have prostate cancer. For example, the chance of prostate cancer is about 10 percent if your PSA is between 0.6 and 1.0 nanograms per milliliter (ng/ml). The risk goes up to about 27 percent if your PSA is between 3.1 and 4.0 ng/ml.

A word of warning: Do not accept a report that your PSA level is “normal.” When your PSA is tested, ask to know the actual number. Then ask your doctor to tell you about the likelihood — in percentages — that you have prostate cancer.

For many years laboratories reported PSA levels of 4.0 ng/ml or lower as “normal.” However, the word “normal” suggests that there is no risk. This is a false suggestion. Prostate cancer is well known in men with PSA levels much less than 4.0 ng/ml. You can see examples in the previous paragraph.

And for those who care, one nanogram (1 ng) = 0.000001 gram (or about 0.0000035 oz), so we are talking tiny levels of PSA. One nanogram per milliliter (1 ng/ml) is the same as 1 gram of PSA in 1000 liters or 1 oz of PSA in 750 gallons of blood.

Recommendations for PSA Testing

Many major medical organizations suggest that doctors discuss the potential benefits and harms of regular PSA testing with their patients, consider the patients’ preferences, and individualize the decision to test. However, medical organizations have also taken contradictory positions.

The different recommendations can be explained by the lack of data to support PSA screening for all men. Data to support the value of early prostate cancer detection with PSA (and physical examination) followed by treatment are starting to emerge. In studies carried out in Washington State, and in Austria, men who had early detection of prostate cancer (using PSA and DRE) went on to receive immediate treatment or active surveillance followed by delayed treatment if necessary. The men who received early treatment lived longer. Also, data from two major randomized clinical trials, reported in early 2009, suggested that there may be a mortality benefit asspociated with mass, population-based screening for prostate cancer. However, this mortality benefit comes with a very high risk for the over-treatment of men who have some (relatively indolent) cancer cells in their prostates but would never actually find this out or need treatment if they didn’t have a PSA test. (More information on the PCLO study and the ERSPC trial can be found elsewhere on this web site.)

Talk to your doctor and make your own decision about the value of PSA testing for yourself (with your doctor’s advice). This decision needs to take into account your personal risk for prostate cancer and the potential need to treat the cancer if it is diagnosed. Here are some general guidelines that may be helpful:

  • It’s not a bad idea to get a “baseline” PSA level taken some time in your 40s. This gives you a reference level for comparison when you get older.
  • If you have specific risk factors for prostate cancer — African American race or a family history of prostate cancer — get that baseline level sooner rather than later.
  • At age 50 it is may be good idea to start getting regular PSA tests. You may not need them every year if you have no known risk factors for prostate cancer. That’s up to you and your doctor. Remember that the PSA test is easy and can be combined with other blood tests, such as a cholesterol level.
  • Above all, remember that no single PSA test result tells you if you have an increased risk for prostate cancer. Your PSA can vary slightly for all sorts of reasons. If it is 0.4 ng/ml for 3 years and then goes to 0.5 ng/ml in the fourth year, this is not a clear signal of risk.
  • If you are in any doubt about what a particular PSA result may imply, always ask your doctor to tell you what he or she thinks in language that you understand.
  • And last but by no means least … A rising PSA, even if leading to a positive prostate biopsy, is not necessarily a signal for an urgent need for treatment — or even a need for treatment at all. See the section on “Treatment: the absolute basics.”
Content on this page last reviewed and updated December 11, 2010.
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