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How do blood tests help diagnose a heart attack?

Blood tests help diagnose a heart attack by revealing the presence of troponin, a product released by heart muscle cells after a heart attack. When muscle cells are damaged they break down and release what was inside the cells. These molecules can be seen in the blood stream. In the setting of a heart attack the heart muscle cells break down and release troponin, which can be seen starting very quickly afterwards and can stay in the blood stream for several hours. This allows doctors to diagnose a heart attack even if symptoms resolve or there are no other positive tests.
Anthony L. Komaroff, MD
Internal Medicine
When heart cells die, they release enzymes, the chemicals that trigger vital tissue functions. Some of these enzymes are specific to the heart and aren't produced in any other tissue in large quantities. Doctors measure the blood levels of these enzymes at intervals over time. Because dying heart cells release different enzymes at different rates, the blood tests can help pinpoint the time the heart attack occurred -- information that is particularly useful when symptoms are vague. In addition, the more cells that die, the higher the blood levels of these different enzymes. Doctors can use this information to estimate the amount of heart tissue that has been destroyed.

If doctors suspect that you are having a heart attack, they will probably test your blood for either troponin I or troponin T, which are proteins that begin to rise within minutes to hours after a heart attack. Troponin levels usually increase sharply about four to six hours after heart muscle has been damaged, reach peak levels in 10 to 24 hours, and return to normal 10 to 14 days later. Another protein in the blood, creatine kinase-MB, also rises in response to heart tissue damage within six hours of a heart attack. It reaches peak levels at about 18 hours and returns to normal in two to three days. Troponin has emerged as the preferred test for heart attacks at most hospitals. Compared to creatine kinase-MB, it is less likely to cause false positives (that is, to mistakenly identify a heart attack when one has not occurred), and it remains elevated for a longer period of time.

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Important: This content reflects information from various individuals and organizations and may offer alternative or opposing points of view. It should not be used for medical advice, diagnosis or treatment. As always, you should consult with your healthcare provider about your specific health needs.