My colleague, Dr. Jeff Carstens, responded to my blog entry dated 2/2/09 regarding the unfortunate demise of noted political commentator Tim Russert. I think his comments are helpful to bear in mind when we think about medical tests in general, and tests for coronary artery disease in particular:
“The accuracy of a regular treadmill without imaging varies from around 65-80%. A large part of how good a test of this type is depends on how likely the patient had a problem to begin with. There are both false positive (the test is abnormal and the patient doesn’t really have a problem) and false negative (the test is normal and the patient does have a problem) considerations. The tests are generally best for people whom you have an intermediate suspicion. A 65 year old obese, diabetic, hypertensive, hyperlipidemic, smoking male with chest tightness that reliably occurs with exertion and goes away with rest is so likely to have obstructive coronary disease that a stress test doesn’t offer much except the likelihood of confusion associated with a false negative test. Similarly a 20 year old woman with no risk factors and no family history of coronary disease who has intermittent sharp stabbing chest pains at rest that last only a few seconds at a time is at higher risk for having a false positive test that will lead to further unnecessary cardiac workups. Mr. Russert was likely in the intermediate category where stress testing can be appropriate but it still remains imperfect and unable to detect the likelihood of a heart attack.”
It would be wonderful if every clinical test we use produced a simple, black-and-white, straightforward answer. Do you have prostate cancer? Yes or no. Will you have a heart attack this year? Yes or no. Unfortunately most of our tests give us a somewhat gray answer. Do you have heart disease? Probably yes or probably no. We then have to use further testing, as well as clinical common sense, to sort out the meaning of the results of the test. This idea of an imperfect screening test is often what is most difficult for patients to understand. It’s also the hardest thing to teach new doctors. I suppose that’s why they still call it the “art” of medicine.