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Cardiac Enzymes


Updated May 28, 2014

Written or reviewed by a board-certified physician. See About.com's Medical Review Board.

Definition: Cardiac enzymes are proteins from heart muscle cells that are released into the bloodstream when heart muscle is damaged, such as during a myocardial infarction (MI). By measuring blood levels of cardiac enzymes, doctors can tell whether heart muscle damage has recently occurred. Therefore, measuring cardiac enzymes is often an important step in diagnosing MIs.

Current clinical practice is to measure two different cardiac enzymes when an MI is suspected: creatine kinase (CK), and troponin (T).

CK is released into the bloodstream 4 to 6 hours after heart cell damage occurs, and peak blood levels of CK are seen after 24 hours. Elevated CK levels usually, but not always, indicate heart muscle damage. CK levels sometimes can be increased with damage to other kinds of cells as well.

T is released into the bloodstream 2 to 6 hours after heart cell damage, and blood levels peak in 12 to 26 hours. Elevated levels of T are regarded as a more reliable indicator of heart muscle damage than elevated CK levels.

Because T is an "earlier" marker of cardiac cell damage than CK, and because it is somewhat more accurate at indicating heart cell damage than CK, T is the preferred marker today for diagnosing MI. Both of these cardiac proteins are routinely measured, however, in patients suspected of having MI.


Thygesen, K, Alpert, JS, White, HD, et al. Universal definition of myocardial infarction: Kristian Thygesen, Joseph S. Alpert and Harvey D. White on behalf of the Joint ESC/ACCF/AHA/WHF Task Force for the Redefinition of Myocardial Infarction. Eur Heart J 2007; 28:2525.

Also Known As: enzymes, cardiac biomarkers

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