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Blood Sample

What is PSA?

PSA stands for prostate specific antigen.  It is an enzyme produced by the prostate and, as far as we know, only by the prostate.  PSA shows up in the bloodstream and we can measure it like we can blood sugar, electrolytes, etc.  It is what we call a “marker” for prostate cancer.  In other words, if the PSA is abnormally high, prostate cancer may be present.

How do We Use PSA?

The PSA blood test is an important part of screening for prostate cancer.  We use PSA to check for the possibility of prostate cancer (see our FAQ on Prostate Cancer Screening).  Although PSA is pretty good for this purpose, as you will see next, it is far from perfect.

The normal range for PSA is from 0.0 to 3.0.  Until recently, the normal range was considered to be 0.0 to 4.0 but most experts now agree that 3.0 is the most appropriate upper limit.  If you want to get into the weeds a bit, here’s what PSA really means:
1.  Men with a PSA in the normal range have less than a 10% chance of having prostate cancer.
2.  With a PSA of 3.0 to 10.0, the risk of prostate cancer is about 20% or 25%.
3.  With a PSA of 10.0 to 20.0 the risk is about 50%.
4.  If the PSA gets above 20.0, almost all of those men have prostate cancer.

Is PSA a Good Blood Test?

Well, yes and no.  While it is true that most men with prostate cancer will have an elevated PSA, it is NOT true that most men with an elevated PSA have prostate cancer.  The reason for this is that there are many things that can cause PSA to go up.  Prostate infections, ordinary enlargement of the prostate, prostate injuries, etc. can cause an elevated PSA.  In fact, the most common reason for PSA to go up is ordinary enlargement of the prostate which happens to all of us as we get older and has nothing to do with prostate cancer.  Generally speaking, only about 20% of men with a slightly elevated PSA actually have prostate cancer.  The other 80% simply have an enlarged prostate, not prostate cancer.

The problem is that, in order to determine whether or not an elevated PSA means prostate cancer and not just ordinary enlargement of the prostate, we must perform a prostate biopsy.  As you can see from the discussion above, perhaps 80% of men with a slightly elevated PSA do not really need a prostate biopsy.  We would like to have a better test for prostate cancer so as to avoid unnecessary prostate biopsies.  Although there are other blood and urine tests for prostate cancer, to date, none of these has proven to be consistently better than PSA.

So, even though PSA is not perfect for screening purposes, it is very useful for monitoring men after treatment for prostate cancer.  Men who have had surgery for prostate cancer should have a PSA of essentially 0.0 thereafter.  Following radiation treatment, the PSA should be less than 0.5.  If the PSA starts to go up after treatment for prostate cancer, we have concerns about cancer recurrence or persistence.
We hope this answers some of your questions about PSA.  Call Gallatin Urology (406-551-2306) for an appointment if you need more information or if you have concerns about prostate cancer.

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