PSA, or prostate-specific antigen, is an enzyme produced mainly by the cells lining the ducts of the prostate. Its job is to help the semen remain in liquid form after ejaculation. Normally, then, PSA is found in significant amounts only in semen or in the prostate gland itself. In the 1980s, however, scientists found a way to detect miniscule quantities of PSA in the blood stream, and, soon after, they observed that, if men had more than a barely detectable amount of PSA in the blood, they were more likely to have prostate problems: an enlarged prostate, for example, or even prostate cancer.

Currently, PSA is measured in nanograms per millilitre. (To give you a reference point, one nanogram is one billionth of a gram (1/1,000,000,000), and it is the average weight of a human cell.) Typically, between 0 and 4 nanograms per millilitre of PSA is considered in the normal range. However, doctors are constantly finding ways to use PSA readings with more accuracy to determine whether a particular man might have early-stage prostate cancer, and they now adjust for factors such as a man’s age; his race, family history of cancer, or other risk factors; and whether there has been an increase in his PSA level since his last test.

Please note: If you do have a higher than normal amount of PSA in your blood, it does not mean that you have prostate cancer. Aging and other conditions, such as benign prostatic hyperplasia (BPH) or prostatitis, can cause abnormally high PSA levels.

Other Articles on PSA Testing from the Archives

Recent PSA Controversy: Our Response
The recent publication of two articles on prostate-cancer screening in the March 2009 issue of the New England Journal of Medicine has spurred renewed controversy over the place of the PSA test in promoting men's health. Our policy on early detection remains unchanged. Click here for more.

More Support for PSA Testing: 2008
Award-winning science writer Tom Keenan argues that provinces should "pony up for prostate tests" that use PSA as an early diagnostic tool. And researchers speculate that the more widespread use of PSA testing in the United States might have resulted in a steeper decline in mortality rates for prostate cancer in that country than in the United Kingdom. Click here for more.

The PSA Test: 2007
The proper role of the PSA test in the early detection of prostate cancer has long been debated, and recent research and events are adding fuel to the discussion. Network representatives lobby politicians and raise public awareness regarding the importance of "getting the test" while, in the scientific community, the debate continues. Click here for more.