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Ultrasound Screening -- Not Such a Good Idea
posted by GJ on February 20, 2008 @ 10:10AM
First off, if you missed it, look below this long post for the update post from Kristen. Now, I get a e-zine from Skeptic Magazine weekly, which usually has a nice column that I enjoy reading, but usually it's very skeptic-centric and would either be totally uninteresting to the rest of you, or fan the flames of, well, you know. It's not like we haven't played out that game often enough here. Anyhow, I'm including this latest one because it's really not about woo, pseudoscience, religion, or any of that. Note the lack of a "woo" tag this time. It's simply an interesting point of view about a procedure that is done all over the country that in all likelyhood, is really just a waste of money. Read on for the details:
Ultrasound Screening: Sometimes Ignorance is Bliss
by Harriet Hall, M.D. 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. The 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 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: - True positive (the test is positive and you have the disease)
- False positive (the test is positive but you don’t have the disease)
- True negative (the test is negative and you don’t have the disease)
- 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 negatives. It makes a big difference how common the disease is in the population being screened. The rarer the disease, the more likely a positive test will be a false alarm. Only 10% of positive mammograms actually turn out to be cancer. 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. His screening test killed him. The U.S. Preventive Services Task Force wrestles with these issues, studies risk/benefit ratios, examines the latest and best research, and makes recommendations for screening the general asymptomatic population. They recommend one-time ultrasound screening for AAA in men between the ages of 65 and 75 who have ever smoked; they recommend against screening in women. They recommend against screening for PAD, because if we find PAD the recommendations are the same ones we make for everyone: smoking cessation and exercise. They recommend osteoporosis screening for women over age 65 (or 60 if they have risk factors). When ultrasound is used for osteoporosis screening, about a third of patients have a positive result that must then be confirmed by a DEXA test; it makes more sense to use DEXA in the first place. When tests fall under the USPSTF recommendations, Medicare and insurance companies usually pay. Carotid artery testing can lead to life-saving treatment for patients who have symptoms, but if you have no symptoms, you may not need treatment. Even if the artery is 60–99% blocked, surgery may only reduce risk of stroke by 1% per year, and the surgical risks may outweigh the benefits. Indiscriminate ultrasound screening is a blunt instrument: it sees a lot of suspicious findings that are due to benign conditions that don’t require treatment. Diagnosing the benign conditions requires more tests, which may be expensive, invasive, and possibly even lead to complications and death. When ultrasound finds something important, it is often something that would have been found later when symptoms developed, and usually finding it sooner makes no difference in survival. And think of all the needless worry! These direct-to-consumer peddlers of ultrasound fail to divulge crucial information; so their customers can’t really give informed consent to a procedure that, while harmless in itself, can lead to various kinds of indirect harm. They play on people’s fears and their desire to take control of their own medical care. They imply a promise of far more than they can deliver. They may not do as much harm as the peddlers of whole body screening CT scans (which involve substantial radiation exposure), but in my opinion, they are just as wrong-headed.
| Tags: medicine, science
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