Dear Dr. B: What is PSA? I believe this a blood test to check for prostate cancer. If this is true then why is my family doctor reluctant to order one for me? Can you please tell me more about this test, who should get it and how often? Yours, worried Mr. P
Dear Mr. P: PSA stands for Prostate-Specific Antigen. Yes, this test is now widely used for early detection of prostate cancer and to follow the progress of patients who have had prostate cancer.
Prostate cancer is now the most commonly diagnosed cancer in Canadian men and second most common cause of death from cancer in men. Prostate gland is present only in men at the junction of the urinary bladder and the urethra. PSA was thought to be produced and secreted solely by the cells of the prostate gland. But this is not true anymore. PSA is also found in breast cancer and other cancers.
Once upon a time, digital rectal examination was the only crude way to pick up early prostate cancer. Then came PSA blood test. PSA was expected to replace the embarrassing and uncomfortable digital rectal examination. And it was promoted as an ideal test for screening and early detection of prostate cancer. But this hope has not materialised. And the controversy continues.
In a recent edition of the Canadian Medical Association Journal, there are two commentaries on this issue. One is written by two family physicians and the other one by a urologist.
The family physicians feel that PSA testing in men over 70 should be avoided. They restrict the use of PSA screening to men between 50 and 70 years of age unless they are at higher risk (e.g. black American men and those with a family history), in which case screening is initiated at 40.
How often the test should be ordered?
According to the family physicians, the literature survey suggests that PSA should be ordered anywhere from every 2 years to every 5 years. Normal value should be less than 4 ng/mL. Another report suggests that men with PSA results of 4ng/mL and below should be tested every 6 months for at least 3 consecutive tests.
Currently, these family physicians recommend PSA every year for eligible patients but feel that screening every 5 years is a reasonable alternative.
The urologists commentary agrees that PSA testing for all men between 50 and 70 is a good idea. But PSA screening every 5 years may be inadequate. The urologist feels that yearly testing is reasonable unless the PSA level is below 1 ng/mL, in which case testing every 2 years is acceptable.
In about 20 percent of patients with normal PSA results, diagnoses of prostate cancer will be missed, which supports the idea that digital rectal examination is an important additional diagnostic tool. But digital rectal examination on its own will miss a substantial numbers of prostate cancers.
The urologist feels that the upper limit of normal (4ng/mL) may be too high and it would be prudent for family physicians to refer patients to a urologist if the PSA result is above 2.5-3.0 ng/mL.
So, Mr. P, have I confused you? If yes, then you are now on par with other doctors! The last word on this subject is yet to come. But I hope this information will help you put your doctors advice in proper perspective.
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