When a person presents to the emergency room with symptoms of acute coronary syndrome (ACS), it is usually not clear whether the person is having a heart attack or unstable angina, or chest pain due to another cause. A number of tests are available to help evaluate whether a heart attack (AMI) has occurred.
Blood tests are usually needed to tell whether a heart attack has occurred. Cardiac biomarkers, proteins that are released when muscle cells are damaged, are frequently ordered to help differentiate ACS from a heart attack. These include:
- Troponin – the most commonly ordered and cardiac-specific of the markers. Blood levels of troponin will be elevated within a few hours of heart damage and remain elevated for up to two weeks. Troponin tests are usually ordered initially in the ER when a person presents with symptoms of acute coronary syndrome and then a few more times in the next several hours to look at changes in concentrations. If levels are normal, then it is much less likely that the symptoms and chest pain are due to heart muscle damage and is more likely that the pain is due to stable angina. A rise and/or fall in the series of results indicates a heart attack.
- A test called high-sensitivity troponin 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 heart injury and acute coronary syndrome 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.
- CK-MB – one particular form of the enzyme creatine kinase that is found mostly in heart muscle and rises when there is damage to the heart muscle cells. This test is performed less frequently now that troponin testing is available.
Other tests that may be performed include:
- Myoglobin – a protein released into the blood when heart or other skeletal muscle is injured; this test is used less frequently now.
- BNP or NT-proBNP – released by the body as a natural response to heart failure; increased levels of BNP, while not diagnostic for a heart attack, indicate an increased risk of cardiac problems in persons with acute coronary syndrome.
Other more general screening tests may also be ordered to help evaluate the person's major body organs, electrolyte balance, blood glucose, and red and white blood cells to see whether there are any excesses, deficiencies, or dysfunctions that may be causing or worsening the person's symptoms. These include:
- Comprehensive Metabolic Panel – a group of usually 14 tests that is used as a broad screening tool to assess the current status of an individual's kidneys, liver, electrolyte and acid/base balance, blood glucose, and blood proteins.
- Complete Blood Count – a test used to screen for a variety of disorders that can affect blood cells, such as anemia and infection.
A range of non-laboratory evaluations and tests may be used to assess chest pain and other symptoms. These include:
- A medical history, including an evaluation of risk factors such as age, coronary artery disease (CAD), diabetes, and smoking
- A physical examination
- An electrocardiogram (ECG or EKG) – a test that looks at the heart's electrical activity and rhythm; the diagnosis of a heart attack may be made by changes seen on an electrocardiogram and by a number of blood tests. An ECG is performed within the first few minutes after a person with ACS arrives in the emergency room. It evaluates heart rhythm and can be used to detect changes that prove that a severe heart attack has occurred. Most commonly, the ECG only confirms that the heart is not getting enough blood or has non-specific changes that do not prove that a heart attack has occurred.
- Continuous ECG monitoring – a person wears a monitor that evaluates heart rhythm over a period of time.
Based on the findings of these tests, other procedures may be necessary, including:
- An exercise stress test
- Chest X-ray
- Radionuclide imaging – a radioactive compound is injected into the blood to evaluate blood flow and examine images of narrowed blood vessels around the heart.
- Echocardiography – ultrasound imaging of the heart
- Cardiac catheterization – in this procedure, a thin flexible tube is inserted into an artery in the leg and threaded up to the coronary arteries to evaluate blood flow and pressure in the heart and the status of the arteries in the heart.
- Coronary angiography – X-rays of arteries using a radiopaque dye to help diagnose CAD; this procedure is performed during cardiac catheterization.
For more information on these, visit the National Heart, Lung, and Blood Institute: How is a Heart Attack Diagnosed?