The Paradox of Medical Testing


Last week two medical organizations released new age guidelines for routine breast cancer and cervical cancer screening. In both cases, the age range over which the tests are recommended was narrowed significantly. Given that many Americans are worried about health care reform limiting their medical coverage, and all of us have a family member or close friend who has suffered the ravages of cancer, the news was not well-received.

Admittedly, it's counter-intuitive to think that fewer tests might lead to better outcomes. After all, tests designed to catch cancer (or any disease, for that matter) at its earliest stage should be a good thing, right?

It all depends on the disease and the particular test that detects it.

Like many things, medical testing is about balancing risks and benefits. Take the pap smear test for cervical cancer as an example. For young women ages 15-19, the odds of getting cervical cancer are very small (approximately 2 cases per 1,000,000 adolescent women tested).  However, the test will incorrectly indicate a potential problem in a healthy individual ~5% of the time (called a false-positive result). So if we test 100,000 young women ages 15-19, 5,000 women will not only suffer the anxiety of a falsely positive result, but will be re-tested and maybe even treated for a disease they don't have.

For older women ages 20-49, however, where the risk is as much as 50-100 times higher, test makes more sense.

There are also inherent risks from tests themselves. Mammograms, designed to detect breast cancer, involve X-rays that damage DNA and can lead to cancer. Though the risk of getting cancer from the test is very, very small, it's not zero. A 1997 study concluded that for every 48.5 lives saved by mammography, one life is lost because of radiation exposure.

Finally, there's the issue of overdiagnosis – aggressively treating slow-growing cancers or diseases that would not otherwise harm you, or might even naturally regress. For cervical cancer screenings, tissue abnormalities detected by pap smear are often removed surgically. Invasive surgery may damage the cervix, increasing the risk of premature labor and other complications associated with childbirth. When you combine the very low cervical cancer risk for teens with the fact that many apparent "precancerous" abnormalities in young women often resolve themselves without medical intervention, it makes sense to not routinely test this population.

None of this is to say that testing is a bad idea. In many cases, it is a life-saver. But each disease, test, and the individual's unique family history need to be considered. We shouldn't be blinded by the idea that testing, in every circumstance and for every age group, is necessarily a good idea.



You raise some excellent posts about the variable results and anxiety of false positive tests.
I'm the editor of a nonprofit website, Women's Voices For Change.
We'd love to have you take a look at some of the writing our medical advisory board has done on the subject of cancer screenings, share your thoughts in the comments, and broaden our discussion.
Here's a roundup of what our medical advisory board has written so far:

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