What are cardiac biomarkers?
Cardiac biomarkers are substances that are released into the bloodstream when heart muscle is damaged or stressed. Measurement of these biomarkers is used to help diagnose, assess risk and manage people with the acute coronary syndrome (ACS), a potentially life-threatening condition characterised by the sudden onset of persistent pain in the chest, one or both arms, shoulders, stomach or jaw, shortness of breath, nausea, sweating and dizziness. The commonest cause of the syndrome is a heart attack (also called a myocardial infarction or MI) in which heart muscle cells die from insufficient blood flow caused by the narrowing or blockage of one of the heart's coronary arteries. However, similar symptoms may be caused by unstable angina and by other cardiac and non-cardiac conditions. Between 60% and 80% of patients taken to hospital with chest pain are found not to have had a heart attack.
Cardiac biomarker tests are requested immediately when a patient with symptoms of ACS is admitted to hospital as an emergency. Together with evidence from an electrocardiogram (ECG) and/or imaging investigations, increasing levels over time of a cardiac biomarker can help to identify those who have had a heart attack, allowing early treatment of their condition. Biomarker measurements are also used to assess the result of treatment with surgery (coronary angioplasty) or ‘clot-busting’ drugs. When the heart muscle’s blood supply is successfully restored, rapidly increasing amounts of biomarker are washed into the blood from damaged heart muscle.
Current cardiac biomarker tests used to help diagnose, evaluate, and monitor individuals suspected of having had a heart attack are:
- Troponin - the cardiac biomarker of choice. A diagnosis of myocardial infarction can be made when raised and increasing troponin levels are found together with clinical evidence of ACS and ECG or imaging evidence of reduced blood supply to heart muscle (ischaemia). Without evidence of ischaemia, possible causes of rising troponin concentrations include myocarditis (inflammation of the heart muscle), acute heart failure, an arrhythmia (abnormal heart rhythm) or pulmonary embolism (blood clot lodged in the lung).
- CK-MB - used when troponin is not available.
Other biomarker tests:
- Myoglobin - not now used for diagnosis.
- BNP (or NT-proBNP) - released from heart muscle that is stretched, so is usually used to recognise heart failure. An increased level after a heart attack implies heart muscle strain and an increased risk of recurrent events.
Phased out biomarkers - these tests are not specific for damage to the heart and are no longer recommended for evaluating people with suspected heart attack: