A Heart Attack, or a Long Run? Blood Tests May Confuse the Two

Photograph by Filip Kwiatkowski for the New York Times.

Imagine you're at work and your doctor's office calls. "We need you to come in immediately for a stress test," the nurse tells you.

A stress test?! you think. I'm a vegan runner with hardly any cholesterol in my body; how could I need a stress test?!

A fascinating article in the New York Times has the explanation. Apparently, it's possible for the body to retain higher-than-usual levels of a heart protein, troponin, for up to 24 hours after vigorous exercise - and sometimes longer. This could falsely indicate a heart attack, and potentially lead to unnecessary medical interventions and wasted medical expenses.

Bottom line: Whenever possible, wait 24 hours after exercising to have blood tests, and if the tests show a higher level of troponin, make sure your doctor knows you're a runner!

Read on below... and see you on the trail!

From the New York Times: The Lab Says Heart Attack, but the Patient Is Fine

By Gina Kolata Published: November 26, 2008

The man was 40 years old and seemed perfectly healthy — he had just run a 10-kilometer race. But he fainted after the race and was rushed to a hospital. There, in the emergency room, his blood was tested. His levels of a heart protein, troponin, were sky-high. It looked as if he was having a heart attack.

The runner ended up in the coronary intensive care unit at Hadassah-Hebrew University Medical Center in Jerusalem. He was in the hospital for four days, undergoing test after test. Yet nothing appeared to be wrong, his doctors — Lior Tolkin, Beth Goldstein and David Rott — report in a recent issue of Cardiology. He had no other symptoms of a heart attack; every test of his heart’s function was normal. And his soaring troponin levels, which can be an indicator of heart muscle damage, went down to normal.

A false alarm or a heart attack averted or maybe a lab error? Researchers say the most likely explanation is that the man had been caught up in a poorly understood but surprisingly common phenomenon: blood tested shortly after a long or strenuous bout of exercise is likely to show abnormalities, maybe even indicators of a heart attack or liver failure. But usually the patient is not in danger. Instead, those results are normal and are not a reason for concern.

While it is unusual to find such effects after a race as short as 10 kilometers, researchers say they are well aware of the general problem.

“I can tell you several stories like that,” said Dr. Fred Apple, a professor of laboratory medicine and pathology at the University of Minnesota School of Medicine.

In one, in fact, he is the center of the story.

Dr. Apple likes to experiment on himself, so one day, when he was a medical resident at Washington University in St. Louis, he drew his own blood and sent it to the hospital lab for routine tests.

The next thing he knew, he was being paged and escorted to the coronary intensive care unit. His blood test results were terrifying, with levels of an enzyme, creatine kinase MB, 10 times higher than normal. Like the runner in Israel, it looked as if Dr. Apple was having a heart attack.

His heart was fine. But Dr. Apple had just gone for a long run (he was running 50 to 60 miles a week in those days).

That experience, in the 1980s, made Dr. Apple curious about lab tests after strenuous exercise, and led him to systematically study the problem, documenting the exercise effect.

“I’d say that 5 percent of people who stress their bodies with exercise could bump up some of these levels above the level that signals a heart attack,” Dr. Apple said.

To avoid false alarms, he suggests that patients avoid lab tests within 24 hours of exercise. If not, he said, “you are asking for abnormalities to be detected.”

Dr. Malissa Wood, a cardiologist at the Massachusetts General Hospital who is a marathon runner, goes further. “I think it’s a really bad idea to have blood work unless something is wrong,” she said.

Dr. Wood and her colleagues have studied runners in the Boston Marathon, testing their blood before and after the race for proteins that can indicate a stroke risk or a heart attack.

“Almost everything we looked at went up,” she said.

And it may not take hours of exercise to do it.

Rob Shave and his colleagues at Brunel University in England recently reported in the Journal of the American College of Cardiology on nine young men who ran a marathon distance on a treadmill. The researchers took blood samples from the men every 30 minutes while they ran and periodically for 24 hours afterward. All had marked increases in troponin within one to two hours after they started running. Everyone’s troponin levels fell within an hour after the run, but in eight of the runners the protein’s levels rose again over the next hours, and five runners had elevated levels 24 hours later.

Yet, Dr. Wood noted, this study involved healthy people. They were not having heart attacks. “Their hearts were fine,” she said.

It is not known for sure why exercise can elicit such strange lab results, researchers say. But part of the explanation is thought to be immune system responses involving inflammation, and part is thought to be effects of temporary skeletal muscle injury.

For example, some studies biopsied the muscles of runners before and after marathons. After the race, muscle fibers were broken and dying. But skeletal muscle is very different from heart muscle. When heart muscle dies in a heart attack, it never regenerates. Skeletal muscle does. Within four days, those runners had repaired their skeletal muscle, growing new muscle fibers to replace the ones that had died.

An echocardiogram also might be misleading. Vigorous exercise can bring on transient abnormalities in the functioning of the left ventricle.

Further complicating the picture is the huge variation from person to person.

“Everyone responds differently,” Dr. Apple said. “Each person is their own little experiment.”

Enzyme levels also soar in people with larger muscles, men as compared with women, blacks as compared with whites. Enzyme levels in a black man after a marathon can be twice as high as those in a white woman, Dr. Apple said.

“I’ll often get a call from a clinic,” asking about lab test results for a black man who recently raced, Dr. Apple said. “I’ll say, ‘That’s normal for a black man.’ ”

Dr. Wood said that athletes and doctors should be wary of blood tests that seem at odds with clinical findings. All too often athletes end up in emergency rooms after races because they are breathing hard or they fainted or their chests hurt (typically because their stomachs are upset). Often, she added, those athletes are just fine.

“We recognize that after a long-distance endurance event the body is going through some sort of adjustment,” Dr. Wood said. “Most of it is a blip on the radar screen.”