Primum no nocere

We've all heard of "First, do no harm," and we assume this is a fundamental principle of medical ethics. It is not. A physician who truly tried to live by that creed would be out of business. Medical intervention in general almost always carries some risk of harm.

For example, David Brenner and Eric Hall in the new NEJM remind us that those quick and easy CT scans, even though they make terrific pictures of our insides that doctors really get hot over, expose us to quite a bit of radiation. In fact, they estimate, up to 2% of cancers in the U.S. may be attributable to CT scans. That probably sounds worse than it really is for various reasons that I won't go into here because I'll do it another time, but still, it obviously isn't a good thing.

That certainly doesn't mean we should junk all the scanners, however, or that you should necessarily refuse one if your doctor thinks it's a good idea. Under many circumstances, a scan might be worth the risk. The issue is to understand the risk/benefit situation (I won't call it an equation or a ratio because it isn't that simple) and to make an informed decision that makes sense in your case. Since people like news you can use I will tell you that the single biggest parameter is age. CT scans create far more lifetime risk for children than they do for people over age 40 or so.

But rather than trying to make decisions based on a blog post, what you need to do is make your doctor look up the relevant information and discuss it with you. Mostly, they don't do that. Indeed, Brenner and Hall write that "In a recent survey of radiologists and emergency-room physicians, about 75% of the entire group significantly underestimated the radiation dose from a CT scan, and 53% of radiologists and 91% of emergency-room physicians did not believe that CT scans increased the lifetime risk of cancer."

I've had two abdomen scans in my life, both of them probably fully indicated, but still, I don't like to hear that. One of the most intractable problems in medicine, it seems, is just getting doctors to pay attention to what they are supposed to know.