Prostate Specific Antigen

Prostate specific antigen (PSA) is a substance made by the prostate gland. Although mostly found in semen, a small amount is also present in the blood. Most men have levels under 4 nanograms per milliliter of blood (ng/ml). When prostate cancer develops, the PSA level usually goes above 4ng/ml but in some cases, the cancer can be present at levels lower than 4. A PSA rise does not automatically mean cancer. PSA also rises when the prostate is enlarged because of benign prostatic hyperplasia, or BPH, and sometimes with prostatitis.

If the level is in a borderline range between 4ng/ml and 10ng/ml, a man has about a 25 percent to 35 percent chance of having prostate cancer. PSA higher than 10ng/ml could mean between a 40 percent and 50 percent chance for cancer, and the risk increases further as the PSA level increases. PSA is an ideal marker for prostate cancer because it's basically restricted to prostate cells.

Most PSA tests measure "total PSA," or the amount that is bound to blood proteins. But some tests measure not only total PSA, but another component called free PSA, which floats around unbound in the blood. Free PSA above 25 percent is a stronger indication that cancer isn't present. Comparing the two tests helps doctors rule out cancer in men whose PSA is mildly elevated from other causes.

The benefits of screening for prostate cancer are still being studied. Scientists are researching ways they can distinguish between cancerous and non-cancerous conditions, those that are slow-growing and fast-growing, and potentially lethal cancers through new PSA testing methods and other tumor markers.

The National Cancer Institute and other medical organizations are conducting the 'Prostate, Lung, Colorectal, and Ovarian Cancer Screening Trial,' or PLCO Trial, to determine whether certain screening tests reduce the number of deaths from these cancers. And the PSA and DRE tests are being studied to see whether yearly screening will decrease a man's chance of dying from prostate cancer.

It's important to remember that sometimes it's better to wait and see whether the cancer is growing slowly and not causing symptoms. More and more doctors are doing that today.  In many cases they are foregoing the PSA test as well.