By Hall, Harriet
Skeptic (Altadena, CA) , Vol. 13, No. 4
Ultrasound Screening: Is Ignorance Bliss?
I never thought I'd be promoting ignorance! I've always thought the more information, the better; but there are exceptions. I'm going to explain something that is very counterintuitive and grates against every fiber of our truth-seeking skeptical brains.
An ad shouts: "Tests That Can Save Your Life ... Stroke is America's third leading killer ... Half of all stroke victims have no warning signs before a stroke occurs." Life Line Screening comes to your community, sets up their ultrasound machines in a church or community center, and offers screening for stroke (carotid artery), abdominal aortic aneurysm (AAA), peripheral arterial disease (PAD), and osteoporosis for $129. The Healthscreens company adds gallbladder, kidney, liver, thyroid, and heart screens for a total of nine screenings for $215. They say "Don't Wait ... Until it's too late!"
A skeptic asks: if these tests save lives, why doesn't my doctor order them, and why doesn't my insurance company pay for them? The ultrasound peddlers answer that doctors don't care about prevention and insurance companies are stingy. That's nonsense. Doctors do care very much about prevention, and insurance companies would save money in the long run by diagnosing things early. Doctors do use these tests to screen patients at high risk and to aid in diagnosis (and when used that way, they are covered by insurance). They just don't use them to screen the entire population of mostly healthy people.
What could be wrong with checking all these areas of your body for potential problems? Wouldn't you like to know if your neck arteries are clogged? Wouldn't you like to know you had an aneurysm that was about to explode? Wouldn't you like to know if there was a lump lurking somewhere in your anatomy? Like almost everyone else, I would like to know those things, but my critical thinking skills have overcome that desire. I wouldn't take those ultrasound tests even if they were free.
Obviously we're not going to do every possible test on every possible person. You could test all 5-year olds for gonorrhea, but you probably wouldn't. What makes a good screening test? The answer depends on the four possible outcomes of any test:
(1) True positive (the test is positive and you have the disease);
(2) False positive (the test is positive but you don't have the disease);
(3) True negative (the test is negative and you don't have the disease);
(4) False negative (the test is negative but you really do have the disease).
A good screening test has a low rate of false positives and false negatives.
It makes a big difference how common the disease is in the population being screened. Only 5% of positive mammograms actually turn out to be cancer. The rarer the disease, the more likely a positive test will be a false alarm. Assuming you find a true positive result, you want it to make a difference. Does early diagnosis prolong your life span, or does it just prolong the time you carry the "sick" label? Is there an effective treatment that will prevent death or improve well-being? Are there risks to the treatment that must be weighed against the benefits?
We no longer do routine screening urinalysis. It wasn't productive. If patients had no symptoms, a urinalysis rarely found anything that mattered, and we wasted a lot of time and effort trying to explain minor transient findings.
We no longer do annual chest x-rays. Why? Because they did more harm than good. There was a small risk from the radiation itself. When a lung cancer was big enough to see on x-ray, it was usually too late for treatment to prolong survival; and we found too many questionable shadows that required further investigation. My father-in-law was a case in point. A routine chest x-ray showed a mass. They operated and found something benign and insignificant, but he had complications from the surgery and died. …