Cardiac markers are substances that are released into the blood when the heart is stressed or damaged. These are often referred to as biomarkers and are helpful in evaluating heart function. The measurements of these biomarkers are vital in the diagnosis of cardiac ischemia and acute coronary syndrome (ACS), these are conditions that are associated with insufficient blood flow to the heart.
Conditions when the heart is under severe stress causes cardiac markers to show up in the blood, for example after a heart attack. In these situations the levels of biomarkers present can be quickly used to find out how seriously the heart was affected and the size of the heart attack.
The cardiac markers listed below are often routinely used in diagnosing a heart attack.
- Cardiac Troponin (TnT and cTn-I): Are the most common biomarkers used, offering the highest sensitivity and are now widely accepted as the best markers for finding a heart attack. Can enter into the bloodstream straight after a heart attack and can stay in the bloodstream for many days, even after all the other biomarkers have returned back to normal levels.
- Creatinine Kinase (CK): The levels of this enzyme can usually double after a heart attack. However, it is not very specific since many other conditions are also known to elevate the levels of CK besides a heart attack.
- Creatinine Kinase-MB (CK-MB): A subtype of CK and is more sensitive for measuring heart damage following a heart attack. Levels of CK-MB are found to rise 3-12 hours after a heart attack and generally return to normal levels are 1-2 days.
- Myoglobin: A small protein that functions in the storing of oxygen, this is not specific in finding a heart attack but is often used alongside troponin to help diagnose a heart attack.
Other proteins which are also useful cardiac markers include C-reactive protein (CRP), ferritin, haptoglobin, cystatin, fibrinogen, homocysteine and natriuretic peptides especially B-type natriuretic peptide (BNP). It is important that cardiac biomarkers are measured in all patients who experience chest discomfort consistent with acute coronary syndrome (ACS). Any presence of elevated levels cardiac enzymes should be interpreted in the context of ECG and alongside clinical findings.