Cardiac Markers

Also Known As: Cardiac BioMarkers

Cardiac biomarkers are substances that are released into the blood when the heart is damaged or stressed. Measurements of these biomarkers are used to help diagnose acute coronary syndrome (ACS) and cardiac ischemia, conditions associated with insufficient blood flow to the heart. Tests for cardiac biomarkers can also be used to help determine a person's risk of having these conditions or to help monitor and manage someone with suspected ACS and cardiac ischemia.

The root causes of both ACS and cardiac ischemia are usually the buildup of plaque in artery walls and hardening of the arteries (atherosclerosis). This can result in severe narrowing of the arteries leading to the heart or a sudden blockage of blood flow through these coronary arteries.

  • Cardiac ischemia is caused when the supply of blood reaching heart tissue is not enough to meet the heart's needs. When not enough blood gets to the heart, it can cause pain in the chest (angina), shortness of breath, sweating, and other symptoms. Typical angina occurs when the coronary arteries have been gradually narrowed over time. The pain starts when a person is active, making the heart work harder, and is quickly relieved by rest or by drugs that increase blood flow to the heart, such as nitroglycerine.
  • ACS is caused by rupture of a plaque that results from atherosclerosis. Plaque rupture causes blood clot (thrombus) formation in coronary arteries, which results in a sudden decrease in the amount of blood and oxygen reaching the heart. A sudden decrease in the supply of blood to the heart can cause prolonged chest pain called unstable angina, often occurring at rest or not relieved by rest or nitroglycerine.
  • When blood flow to the heart is blocked or significantly reduced for a longer period of time (usually for more than 30-60 minutes), it can cause heart cells to die and is called an acute myocardial infarction (AMI or heart attack). This leads to death of the affected portion of heart muscle with permanent damage and scarring of the heart and sometimes can cause sudden death by causing irregular heart contractions (arrhythmia). Unstable angina and AMI are together called acute coronary syndrome since they are both due to a very acute decrease in blood flow to the heart.

The symptoms of ACS and cardiac ischemia can vary greatly but frequently include chest pain, pressure, nausea, and/or shortness of breath. Though these symptoms are most often associated with heart attacks and angina, they may also be seen with non-heart-related conditions.

It is important to distinguish heart attacks from angina, heart failure, or other conditions that may have similar signs and symptoms because the treatments and monitoring requirements are different. Cardiac biomarker tests are ordered to help detect the presence of ACS and cardiac ischemia and to evaluate their severity. Increases in one or more cardiac biomarkers in the blood can identify people with ACS or cardiac ischemia, allowing rapid and accurate diagnosis and appropriate treatment of their condition.

For ACS, prompt medical intervention is crucial to prevent death and to minimize heart damage and future complications. Cardiac biomarker tests must be available to a health practitioner 24 hours a day, 7 days a week with a rapid turn-around-time. Some of the tests may be performed at the point of care (POC) - in the emergency department or at a person's bedside. Usually, multiple cardiac biomarker tests are done over several hours to ensure that a rise in blood levels is not missed and to estimate the severity of a heart attack.

The Tests

Only a few cardiac biomarker tests are routinely used by physicians. The current biomarker test of choice for detecting heart damage is troponin. Other cardiac biomarkers are less specific for the heart and may be elevated in other situations such as skeletal muscle injury.

Current cardiac biomarker tests that may be used to help diagnose, evaluate, and monitor individuals suspected of having acute coronary syndrome (ACS) include:

  • Troponin (I or T) - this is the most commonly ordered and most specific of the cardiac markers. It is elevated (positive) within a few hours of heart damage and remains elevated for up to two weeks. Rising levels in a series of troponin tests performed over several hours can help diagnose a heart attack.
  • High-sensitivity troponin - this test detects the same protein that the standard test does, just at much lower levels. Because this version of the test is more sensitive, it becomes positive sooner and may help detect ACS earlier than the standard test. The hs-troponin test may also be positive in people with stable angina and even in people with no symptoms. When it is elevated in these individuals, it indicates an increased risk of future heart events such as heart attacks. Currently, this test is not approved in the U.S., but research is ongoing and it may become available in the near future. It is already routinely used as a cardiac biomarker in clinical practice in Europe, Canada, and other countries as well.
  • Creatine kinase (CK) and CK-MB - in the U.S., CK has been largely replaced by troponin. It may sometimes be used to help detect a second heart attack that occurs shortly after the first. CK-MB is one particular form of the enzyme creatine kinase that is found mostly in heart muscle; it rises when there is damage to the heart muscle cells and may be used in follow up to an elevated CK and/or when the troponin test is not available.
  • Myoglobin - this test may be used along with troponin to detect a heart attack early, but in the U.S., it is used less frequently.

Other biomarker tests that may be used include:

  • hs-CRP - this test may be used to help determine risk of future heart attacks in people who have already suffered one in the past.
  • BNP (or NT-proBNP) - although usually used to recognize heart failure, an increased level in people with ACS indicates an increased risk of recurrent events.

On the horizon: several biomarkers are being investigated for their potential use in helping to evaluate people for ACS. These are currently only used in research settings and are not available in clinical practice.

General lab tests are frequently ordered along with cardiac biomarkers to evaluate a person's general health status and the current status of the individual's kidneys, liver, electrolyte and acid/base balance, blood sugar, and blood proteins. They may include:

  • Blood gases
  • Comprehensive metabolic panel (CMP) or basic metabolic panel (BMP)
  • Electrolytes
  • Complete blood count (CBC)

Non-laboratory Tests

These tests allow health practitioners to look at the size, shape, and function of the heart as it is beating. They can be used to detect changes to the rhythm of the heart as well as to detect and evaluate damaged tissues and blocked arteries.

  • EKG (ECG, electrocardiogram)
  • Nuclear scan
  • Coronary angiography (or arteriography)
  • Echocardiogram (Cardiac echo, transthoracic echocardiography (TTE))
  • Stress testing
  • Chest X-ray

For more about these, visit the Non-Invasive Tests and Procedures article on the American Heart Association web site.

These tests are used to help diagnose, evaluate, and monitor people suspected of having Acute Coronary Syndrome (ACS).


Cardiac Troponin

Regulatory protein complex; two cardiac-specific isoforms: T and I Heart Injury to heart 3 to 4 hours Remains elevated for 10 to 14 days Diagnose heart attack, risk stratification, assist in deciding management, assess degree of damage

High-sensitivity cardiac troponin
Currently not approved in U.S. but may be soon; it is routinely used in Canada, Europe

Same as above, just measures the same protein at a much lower level Heart Injury to heart Within 3 hours of onset of symptoms Same as above Same as above; may also be elevated in stable angina and people without symptoms and indicates risk of future cardiac events (e.g., heart attacks)


Enzyme; total of three different isoenzymes Heart, brain, and skeletal muscle Injury to skeletal muscle and/or heart cells 3 to 6 hours after injury, peaks in 18 to 24 hours 48 to 72 hours, unless due to continuing injury Frequently performed in combination with CK-MB; sometimes to detect second heart attack occurring shortly after the first


Heart-related isoenzymes of CK Heart primarily, but also in skeletal muscle Injury to heart and/or muscle cells 3 to 6 hours after heart attack, peaks in 12 to 14 hours 48 to 72 hours, unless new or continuing damage Less specific than troponin, may be ordered when troponin is not available


Oxygen-storing protein Heart and other muscle cells Injury to muscle and/or heart cells 2 to 3 hours after injury, peaks in 8 to 12 hours Within one day after injury Used less frequently; sometimes performed with troponin to provide early diagnosis

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