For any medical test to be useful, it must be both accurate and reliable. There may be a rare occasion when, for a limited purpose, either accurate or reliable might be acceptable. There aren’t any situations, however, when a test that is neither accurate nor reliable would be of any use to a doctor or the patient being treated.
The PSA screening test that, for years, has been one of the main tools for diagnosing prostate cancer has always been regarded as both accurate and reliable. Now, as it turns out, it may be neither.
A study of over 18,000 men done at the University of Texas Health Science Center at San Antonio, and published in the July 6 issue of the Journal of the American Medical Association (JAMA), made some startling findings. In broad terms:
• The test produces numerous “false positives” which means many men who do not have prostate cancer will think they have it and may undergo other tests including an unpleasant biopsy procedure before learning they have no malignant tumor.
• The test produces numerous “false negatives” which means many men who think they are “cancer free” are not. Obviously, such a situation will produce
• When PSA levels appear safely below in the “normal” range of 4, men have been found to have prostate.
• When some men had high PSA levels they were found not to have prostate cancer.
The researchers stressed that men should not treat a PSA screening test as conclusive of anything in and of itself. Rather, a PSA level, whatever it may be, should be regarded as simply one component of a broader picture to be considered along with known risk factors. PSA, like blood pressure and cholesterol readings, should be regarded as “showing a range of risk” only.
Although further research is needed to confirm all of the findings, there is enough evidence of the fallibility of the test to challenge the notion of a “normal” PSA level. Instead, doctors should see a continuum of risk regardless of the particular PSA level.
According to the American Cancer Society, prostate cancer strikes some 200,000 men each year in the U.S. alone killing approximately 29,000 of them. Often this type of cancer is slow-growing and not likely to cause death. Thus, while there is a 17% chance of developing prostate cancer, there is only a 3% risk of actually dying from it.