Stress Tests Good, But Not Perfect

Q:  A few months ago I was having chest pains, so my doctor ordered a stress test. Because it was "positive," he sent me to a cardiologist, who did an angiogram. The angiogram was "negative," showing no signs of blockage of the arteries to my heart.

My cardiologist explained that I had a "false positive stress test." How can that happen? I went through a lot of expense and worry for nothing.

A:  Unfortunately, "false positive" tests happen all the time. The reason is that few tests are perfect, and that includes stress tests.

I don't know which kind of stress test you had; some are more accurate than others. All stress tests try to detect blocked coronary (heart) arteries, but their accuracy differs based on how any artery blockages are measured.

In an EKG stress test, the health of the arteries is measured with an EKG (electrocardiogram) signal. When the test is positive, it's correct about 85% of the time and wrong about 15% of the time (a "false positive").

In imaging stress tests, the health of the arteries is measured with an EKG signal and either (1) a scan after injecting a radioactive marker, or (2) an echocardiogram (or ultrasound of the heart). When these stress tests are positive, they're correct about 90% of the time and wrong about 10% of the time, but they're more expensive and take more time.

Because we know stress tests aren't perfect, doctors routinely follow a positive stress test up with an angiogram, which is 99% accurate.

An angiogram involves putting a needle in the large artery in your groin and injecting a dye that travels into the heart arteries; the dye can be seen by x-ray so the doctor can visualize the health of the arteries. Angiograms have some risks (bleeding in the groin, x-ray exposure, and harm to the kidneys) and might be expensive, so you don't want this test if you don't have a good reason.

Be sure your doctor explains the reasons for tests before you have them. He may have been able to lessen your worry.

Julie L. Mitchell, MD, MS, is an Assistant Professor of Medicine at the Medical College of Wisconsin. She practices at the Froedtert & The Medical College of Wisconsin General Internal Medicine Clinic - East. Her column appears in the Milwaukee Journal-Sentinel.