Cardiac Enzymes

Authored by , Reviewed by Dr Adrian Bonsall | Last edited | Meets Patient’s editorial guidelines

Cardiac enzymes are substances released by the heart muscle when it is injured - for example, during a heart attack or a severe case of angina.

A heart attack (myocardial infarction) can present in many ways, the most common of which is chest pain. Taking blood tests for heart enzymes can help to make the diagnosis of a heart attack.

Patients presenting with chest pain or shortness of breath to healthcare professionals is very common. There can be many causes of these symptoms. Cardiac enzymes are substances released by the heart muscle when it is injured - for example, during a heart attack (myocardial infarction) or a severe case of angina. There are a number of cardiac enzymes and the most common of these is called troponin. There are two types of troponin that can be measured from a blood sample: T and I. Most hospitals will usually only measure one or the other, and both are equally sensitive. Often patients may require a repeat blood test several hours after the first, especially if the first one is negative.

Before troponins, different blood tests were checked looking for heart muscle damage. This included creatine kinase-MB (CK-MB); however, such tests have been outdated by troponins.

Troponin is a protein released from the heart cells when they are damaged. It is only found in the heart muscle, making it useful in diagnosing damage to the heart muscle. It is important that the blood test result be viewed in conjunction with what the patient has presented with and the heart tracing (12-lead electrocardiogram, or ECG). Taken together these three factors will help make an accurate diagnosis.

Once heart muscle damage occurs, it can take 3-12 hours for the troponin level to increase in the blood. It will usually peak at around 24-48 hours and then gradually return to normal over 5-14 days. Many hospitals will measure troponin after 4-6 hours of the onset of symptoms, and some will run a repeat test after 12 hours. The level of the troponin is directly related to how much heart muscle has been damaged. This means that the higher the level of the troponin, the greater the level of heart muscle damage. The higher the level in a heart attack, the greater the risk of a worse outcome.

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