March 16, 2009 -- Question: What is a prostate-specific antigen (PSA) test, and what is a normal PSA level?
Answer: The prostate-specific antigen has been a test that's been around for a little over 25 years. It's a simple blood test. So we basically take a sample of blood and you look for a protein that's basically produced by the prostate. The problem is people think a PSA or prostate-specific antigen equals prostate cancer. It actually is something that's normally expressed in the prostate. So it's not really something unique to cancer, but we do find it in the blood when patients have cancer often.
There's a couple problems, one of which is that many of the things that happen to your prostate as your age also cause your PSA levels to increase. And so this causes many men that have elevated PSA levels to be falsely elevated -- that is not caused by prostate cancer. In fact, it's wrong 80 percent of the time.
On the other hand, about 15 percent of prostate cancer cases do not have elevated PSA levels. They have normal PSA levels.
The question of what would be a normal cutoff of PSA is actually a very difficult one. First we had used 4.0 nanograms per ml, which is the amount of protein that's there, it's PSA protein per milliliter of your blood, amount of blood. But then it was lowered to 2.5, showing that we could then pickup some more men with prostate cancer. But from a study that was done by the Prostate Cancer Prevention Trial, even men that had PSA levels less than one still have a reasonable chance of having prostate cancer. So there's probably no safe single level. It really should be done on a prospective basis, looking at what's normal for an individual.