If you are having chest pain that may be due to a heart attack.
A blood sample taken from a vein in the arm
Troponins are proteins in muscle fibres that help to regulate muscle contraction. There are three different troponins: skeletal muscle troponin C (TnC) and two heart muscle troponins, cardiac troponin T (cTnT) and cardiac troponin I (cTnI). When there is damage to heart muscle, cTnI and cTnT are released into the blood.
How is the sample collected for testing?
A blood sample is taken by needle from a vein in the arm.
Is any test preparation needed to ensure the quality of the sample?
No test preparation is required.
How is it used?
Troponin tests are used, together with an electrocardiogram (ECG), in people with persistent chest pain taken to hospital as an emergency to see if they have had a heart attack, have unstable angina or have a problem outside the heart. In a heart attack a blood clot stops the normal flow of blood and oxygen to the muscle. Without oxygen the heart muscle cells die and release troponin into the bloodstream. The more extensive the damage is, the greater the release and the higher the blood concentrations become. Concentrations can increase within two or three hours and may remain high for 10 to 14 days.
Until recently a standard cTnI or cTnT troponin blood test would have been used by the laboratory, but these two tests are rapidly being replaced by the more sensitive and reproducible high-sensitivity troponins, hs-cTnI or hs-cTnT. An alternative marker of heart damage, CK–MB, is used occasionally when a troponin test is not available. Troponins are the preferred tests for a suspected heart attack because they are more specific markers of damage to the heart, and the concentrations remain elevated in the bloodstream for longer periods of time.
When is it requested?
The diagnosis of acute heart muscle damage requires an increase in the troponin concentration with time. If a high-sensitivity cardiac troponin (hs-cTn) test is used, a second specimen is taken in three hours or so after admission. If the three hour value shows a significant increase of 20% or more, heart muscle damage is confirmed. Otherwise a third specimen is taken after another three hours. With a standard troponin (cTn) test a second sample needs to be taken six to nine hours after admission and sometimes a further sample is needed after 12 -24 hours. Usually a clinical decision can be made more quickly with an hs-cTn test. Not all laboratories in the UK currently offer the hs-cTn test.
In patients with stable angina, a troponin test may be requested if the pain get worse, if it appears when the patient is resting or if the pain does not get better following treatment. These are all signs that the angina is becoming unstable, which increases the risk of a heart attack or other serious heart problems in the near future.
What does the test result mean?
With standard cardiac troponin (cTn) blood tests, normal concentrations of troponin in the bloodstream are so low that they cannot be measured. However, with high-sensitivity (hs-cTn) tests values can be measured in more than 50% of apparently healthy people so that an upper limit for the reference range can be determined.
Even a small rise in troponin may indicate some damage to the heart. When a patient has a large increase in troponin concentration, then it is highly likely that they have had a heart attack or some other form of heart damage. If a patient with chest pain and known stable angina has a normal and stable hs-cTn troponin result, it is likely that their heart has not been damaged.
Increased troponin concentrations should not be used by themselves to diagnose or rule out a heart attack. A physical examination, clinical history and electrocardiogram (ECG) or imaging investigations are also essential. The internationally agreed definition of heart attack requires evidence of a significant increase in troponin (or CK-MB) concentration with time together with evidence of a sudden reduction of heart muscle blood supply (ischaemia) from characteristic symptoms of the acute coronary syndrome (ACS) and new ECG changes or new imaging changes.
Without evidence of ischaemia, possible causes of rising troponin values include myocarditis (inflammation of the heart muscle), acute heart failure, an arrhythmia (abnormal heart rhythm) or pulmonary embolism (blood clot lodged in the lung). Elevated but unchanging values may be seen in chronic heart failure, high blood pressure (hypertension), severe infections, kidney disease and some chronic inflammatory conditions of muscle.
Is there anything else I should know?
The test is not generally affected by damage to muscles other than the heart, so injections into muscle and accidents or drugs that damage muscle do not normally affect troponin concentrations.
What does heart attack mean?
Heart attack means that some of the muscle in your heart has died. The medical term for this is myocardial infarction. Most commonly, a heart attack starts with a feeling of heavy pressure or pain in the chest, often extending into the neck or left arm. You may have trouble breathing, and may feel weak and break into a cold sweat.
A heart attack usually occurs because one of the blood vessels (called coronary arteries) that carry blood to your heart muscle is blocked. This happens when a blood clot forms in a blood vessel that is already partially blocked. The partial blockage is usually due to atherosclerosis (often called hardening of the arteries). This partial blockage occurs gradually over many years as lipid plaques are deposited along the walls of the blood vessels. These plaques narrow and stiffen the arteries and can break apart unexpectedly and then totally block the affected artery.
If I have chest pain, does that mean I am having a heart attack?
Many other problems can cause chest pain, and it is not always possible to tell from the type of chest pain whether or not you are having a heart attack. Many people have chest pain from straining the muscles in their chest, from heartburn or other problems involving the stomach and the tube which carries food into the stomach (oesophagus), from emotional stress and with some lung problems. Chest pain can be a warning sign of hardening of the arteries of the heart often called coronary artery disease (CAD). Chest pain that occurs during exercise, hard work, or at times of stress, lasts for a few minutes and goes away with rest is called angina. If the pain lasts longer than just a few minutes, especially if it occurs when you are resting, seek immediate medical attention.
What if I'm not sure I'm having a heart attack?
If you have prolonged chest pain, especially if it does not go away with rest or if you have been told you have angina, and the drugs you were prescribed do not ease the pain, seek immediate medical attention.
Elsewhere On The Web
British Heart Foundation: Tests for Heart Conditions
NHS Choices: Diagnosing a Heart Attack
IFCC: Implementing high sensitivity cardiac troponin assays in practice - pocket format
IFCC: Using high sensitivity cardiac troponin assays in practice - pocket format
IFCC: Calculating serial change values for high-sensitivity cardiac troponin assays
IFCC: Using high sensitivity cardiac troponin assays in practice