Up to 2 out of 3 U.S. adults had a test in the last few years that exposed them to radiation, researchers estimate. And for a smaller number of people, that may increase their risk of cancer. A new study looked at insurance claims for nearly 1 million adults under 65. For most people, radiation exposure was low. But for 20% who had exposure, the levels were moderate. And for 2% the exposure was high. About 71% of the tests were regular X-rays. But they contributed only 11% of the radiation from medical tests. About 21% of the tests were computed tomography (CT) scans or nuclear imaging. They provided 75% of total radiation. CT scans use far more radiation than regular X-rays. Nuclear imaging uses a small amount of radioactive materials. The study was in the New England Journal of Medicine. The Associated Press wrote about it August 27.

By Robert H. Shmerling, M.D.
Harvard Medical School

What Is the Doctor's Reaction?

It's not really news that radiation from medical tests could harm your health.

That's the reason you're given a protective "apron" when you have X-rays. It decreases the amount of radiation that nearby organs receive. But the risk from chest X-rays and most other medical imaging tests is considered quite small. And it's a risk worth taking if the test provides information that can improve your health.

We've also long known that high doses of radiation can be deadly. Perhaps the most dramatic examples come from Japan. Years after nuclear bombs exploded over Hiroshima and Nagasaki, survivors had a greatly increased risk of cancer related to radiation exposure.

But what is new and worrisome is the recent dramatic increase in medical testing that uses radiation.

A new study of this issue is in the current edition of the New England Journal of Medicine. Researchers looked at insurance claims for nearly 1 million U.S. adults. They found that:

• Almost 70% of those surveyed had at least one medical test involving radiation exposure within the prior 2 years
• The radiation exposure associated with testing was nearly twice what people normally get (such as from the sun)
• Women and older adults had the most radiation exposure

The largest sources of radiation from medical testing were computed tomography (CT) scanning and nuclear stress testing. Doctors order these "high-radiation" tests much more often now than in the past. The number of CT scans has quadrupled in the last 25 years. Nuclear stress tests increased by more than 6% each year throughout the 1990s.

Another recent study estimated that up to 2% of cancers are caused by radiation from medical testing. We know that radiation can be dangerous in high doses. But no one really knows how much risk people face from the radiation in medical tests. That makes it hard to know how worried we should be about this new study. Still, it makes sense to limit your radiation exposure from medical tests if you can.

What Changes Can I Make Now?

There's little doubt that medical imaging can be helpful, especially in emergencies. For example, a head CT can show bleeding that will soon be fatal unless surgery is performed. But most medical imaging tests are not performed in emergency situations. And we don't even know if the increased testing in recent years is helping to improve health.

If your doctor recommends that you have a test, get answers to these questions:

• What's the purpose of the test? If you don't understand why a test has been recommended, ask the doctor to explain.



• How might the results of the test affect treatment? For example, if you have typical symptoms of migraine headaches, a head CT is unlikely to be helpful. But if you've recently had a major head injury, the risks and benefits of having the scan are much different.



• Is the test likely to provide a definite answer? Many tests provide a lot of detailed information but cannot tell you exactly what is causing your symptoms. For example, this occurs often among people with back pain who have many imaging tests.



• Is it safe and reasonable to delay the test? Many symptoms go away on their own soon after they appear. Waiting a short while before scheduling a test can often make the test unnecessary.



• Are there risks or costs to the test? Some insurance plans will not cover tests. Many people find this out only after the test has been performed. Besides radiation, find out whether the test has other risks.

Just last week, the National Institutes of Health Clinical Center in Bethesda, Md., announced that it will start tracking radiation. The hospital will use new scanners that can record how much radiation each patient receives from tests. This information will go into patients' records and can be tracked over time.

This type of system not is widely available, however. So be sure to let your doctor know if you've had medical imaging tests in the last year or two. Individual tests are generally considered safe. But total radiation exposure can add up quickly if you're having many tests or if the tests are being repeated.

What Can I Expect Looking to the Future?

As I read about this new study, two questions came to mind:

• Is the amount of radiation exposure from medical testing truly harmful?
• Are the rising numbers of medical tests worthwhile? That is, do they lead to better health, higher quality of life or longer life?

I hope that research soon will provide definite answers to both of these questions.