Are screening tests good for you?

January 2, 2014 — Leave a comment

If we had a serious disease, we’d like to learn about it before we even had symptoms (so we could get started on treatment). And most of us would like to know if we were at risk of developing a serious disease (so we could make changes to prevent the disease). Right?

Two recent articles in the NY Times point out the problems with screening tests.

An  Op-Ed by H. Gilbert Welch discusses the problems with mammography. If you could find out that you had a small breast tumor before you could even feel it, why wouldn’t you do it? The answer is, “it’s complicated”.

Screening tests are great if they are perfect tests – if there are no false positive tests (where you are told you have the disease but you really don’t) and no false negative tests (where you are told you don’t have the disease but really do). Unfortunately very few tests are that good. Welch estimates that if you were to perform mammograms on one thousand 50-year-old American women every year for 10 years, about half of the women would have false positive tests. Many of these women would have a normal follow-up test – with an ultrasound, biopsy, etc. – but they would have been through significant stress in the process.

We may also be overdiagnosing breast cancer with mammography – finding things that would not be likely to cause any problems in the future. More women may be getting unnecessary surgery, radiation and chemotherapy as a result of mammography than the number of women whose lives are being saved. The problem with overtreatment is not only that it costs money, causes stress and wastes time but it can also have side effects.

In the second article, Kira Peikoff shares her experiences with genetic testing. The author, a 28-year-old woman with a family history of heart disease, rheumatoid arthritis, Alzheimer’s disease and breast cancer wanted to get her DNA tested to see if she was at risk of these diseases. She ordered DNA tests from 3 different companies – Genetic Testing Laboratories, Pathway Genomics and 23andMe. The results from the 3 sources were completely different from each other. After spending hundreds of dollars and waiting months for the results, she had no idea if she was at risk of developing any serious diseases. Clearly, DNA testing has a long way to go before the results are helpful to individuals. But how was she to know that?

Mammography has been around for a lot longer than personalized DNA testing. But even with mammography, the downsides are much less obvious than you might think. When you have a disease, you need to decide which treatment is best for you. The decision to get screened for a disease is also personal. The problem is that in order to make an informed decision, we need to understand the tests better. Unfortunately, even doctors don’t always understand risk very well and they have no incentive to spend lots of time trying to explain it to us.

We need find better ways to explain the evidence for screening tests so that patients can make the best decisions for them.

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