At Risk: The True and False Promises of Medical Screening

Sept. 26, 2008— -- 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

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 Testing

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.

In a clinical trial in Scandinavia, a great number of aging men were divided into two groups. Those who were offered and opted for surgery for their elevated PSA gained very little for the experience compared to those who were not offered surgery. They gained too little for me to opt for the surgery if my PSA was elevated. Therefore, I won't let anyone check my PSA. You need to have this discussion with your doctor before you opt to have a screening PSA.

Colonoscopy

A few rare families and rare diseases aside, colon cancer is another disease of the sunset years.

Like prostate cancer, it is slow to grow and slow to spread but it is far less common than prostate cancer. The treatment, surgical removal, has far less likelihood of complications than prostate surgery.

The screening is not a blood test; it's hunting for the cancer directly. More and more, this is done by inserting a tube into the colon and looking inch-by-inch. It's not a perfect test, requiring patience as much as dexterity.

And it has complications, many of which relate to the removal of polyps which are grape-like growths on a stalk that have very little potential for harm (if they develop into cancer at all, it takes decades).

So we are back to our critical question. The issue is not whether one can find a cancer and remove it, but whether one can find and remove the cancer that is likely to cost me time on this earth.

I don't care if I develop colon cancer in my 80s; something else is likely to kill me long before it can. I don't care if I develop colon cancer in my 70s either, for the same reason. Furthermore, screening me in my 40s is largely an exercise in futility; colon cancer is so very, very rare in 40-year-olds that the chances of a complication of colonoscopy far outweighs the chances of finding the rare cancer. It's in the 50s and 60s that finding and removing the rare colon cancer is likely to be meaningful to that person and worth the risks to all those who don't have colon cancer.

Hence, I had my one colonoscopy. In fact, I settled for a partial look (flexible sigmoidoscopy) because that was good enough risk assessment for me and the procedure is gentler and safer.

I am not alone in realizing the limitations of these tests and others such as mammography or even the annual physical examination. Many a researcher has been recruited to the task of improving screening tests. However, until we have much better screening tests, no person should be screened unaware of the limitations of the test.

Dr. Nortin Hadler is professor of medicine and microbiology/immunology at theUniversity of North Carolina at Chapel Hill, and an attending rheumatologist at University of North Carolina Hospitals. He is the author of Worried Sick: A Prescription for Health in an Overtreated America and The Last Well Person.