A stress test can be used to identify heart problems and other health issues. One type of stress test is performed on a treadmill while technicians gradually increase speeds and inclines and monitor your heart's response. Though your test results may be positive -- indicating a possible problem -- or negative -- indicating no problem -- more tests may be needed to definitively rule out cardiac disease. A stress test can give both false-positive and false-negative results, though technicians take measures to eliminate causes that might lead to a false test result.
If a stress test is positive, it is showing heart problems such as rhythm abnormalities, high blood pressure or chest pains. False-positive results are identified when the stress test is followed up with a cardiac catheterization procedure that does not show heart problems. Since stress tests are only 60 percent accurate, according to Kathy Magliato, cardiac services director at the Santa Monica Saint John's Health Center, it is not uncommon for a patient to be given medications unnecessarily or to undergo surgeries he doesn't need. A false-positive result may also be caused by a known EKG segment abnormality, by use of the heart medication digitalis, by an enlarged heart ventrical or a disease of the heart muscle.
If you receive a negative result from your stress test, your heart is considered to be of normal health. If a heart attack occurs, or blocked arteries are found during a follow-up procedure, the results are then changed to false-negative. The problems with a false-negative are obvious and serious -- you may not get the help you need for undetected heart conditions, which can lead to complications such as a heart attack.
A false-negative result may be a problem with the test itself. The stress test employs a gradual warmup which may give the patient with narrowed arteries time to adjust to the increase in work load. The body adapts to the exercise and the narrowed arteries may not show up during the short-duration test. A nuclear stress test, in which a small amount of a radioactive substance is injected into the veins for imaging, may provide a better testing option if you receive a false result, but false tests results can occur with this type of testing, too. According to the "Journal of Family Practice," in some treadmill cases, the cardiac workload never gets high enough to show a problem, such as lack of blood flow to the heart.
Women have a higher prevalence of false results from stress tests. One of the reasons is that, when women have heart disease, it often affects the smaller veins and arteries in the heart which go undetected during a stress test. Another reason is that breast tissue can set off a false-negative result. If that isn't enough, the presence of estrogen also has an effect on the heart cells.
The heart of an athlete becomes more efficient with training. The heart pumps out more volume with each beat and may have an increase in mass. According to the American College of Sports Medicine, an athlete's stress test results may show blocks, deviations and repolarization abnormalities, which are normal variants. These variants are diagnosed according to the general population, however, and may read as a false-positive test.
- Chicago-Tribune: Demystifying the Cardiac Stress Test
- ACSM's Sports Medicine: A Comprehensive Review; American College of Sports Medicine
- Fitness and Health; Brian J. Sharkey and Steven E. Gaskill
- The Journal of Family Practice: Optimize Your Use of Stress Tests: A Q and A Guide