Most of us believe that when a doctor orders screening tests, that's a serious step toward keeping illness at bay. The screening test can find factors that place us at risk for diseases we might develop in the future or find hidden diseases. In either case, we will be treated.
Screening tests are considered a triumph of modern public health medicine. I only wish it was that straightforward.
It turns out that many of the commonly recommended screening tests fall far short on this promise. They fall so far short that no one should have them without first discussing them with their doctor.
If you are not convinced you will be advantaged by having the test, why bother?
Let me illustrate this with three of the commonly recommended tests. I will explain why I have never let anyone check my cholesterol or my PSA, and why I have submitted to colonoscopy once, and never again.
Blood cholesterol level is a risk factor for heart and other blood vessel diseases -- but not much of a risk factor. If you have the worst LDL and HDL cholesterol we find occasionally in the population, you have a year or two of life expectancy at risk.
For nearly all who are told they have "high" cholesterol, the amount of time on earth that they are risking is measured in months. I'm not sure we can even measure such a small risk, or that I care.
But if you do, the next question is crucial. Can we do anything to my cholesterol that reduces the risk? That's not the same question as can you lower the cholesterol? We can do that very well, and we do lower the cholesterol of millions of Americans thereby reducing the risk factor. But does that reduce the risk?
There are scientific studies asking this question. The treatment does not reduce the risk of dying from heart disease. The most optimistic analysis of these scientific studies leads to the following conclusion: 250 people who have not had a heart attack would have to swallow a statin drug every day for five years to spare a heart attack.
Do you believe we can even measure such a tiny effect? Is it worth your while to take these pills for years? Would it be worth it if you had to pay out-of-pocket?
PSA stands for Prostate Specific Antigen. It's a normal protein in the prostate. A small amount gets into the bloodstream normally.
Greater amounts get into the bloodstream if the prostate is inflamed by infection. Prostate cancer is another cause of more PSA getting into the bloodstream.
Prostate cancer is a normal part of aging; by age 70, essentially all men have prostate cancer. Furthermore, nearly all men will die with their prostate cancer and not from it.
The challenge for screening is not to find prostate cancer, but to find the prostate cancer that will kill a man before his time. That's a tall order, and one for which PSA screening is a double-edged sword. After all, if you want to be sure you will not die from prostate cancer before your time, you will have to submit to a procedure, usually a major surgical procedure that offers a 15 percent likelihood of incontinence and more of impotence.