From the Guidelines
Cardiac enzymes, particularly troponin, are the most reliable biomarkers for diagnosing heart damage, such as myocardial infarction, and should be measured at presentation and 3-6 hours after symptom onset in all patients with suspected acute coronary syndromes. The most important cardiac enzymes include troponin (I and T), creatine kinase-MB (CK-MB), and myoglobin. These enzymes serve as biomarkers that help diagnose heart conditions, particularly heart attacks (myocardial infarction) 1. When heart cells are injured, these enzymes leak into the bloodstream, causing their levels to rise above normal.
Key Cardiac Enzymes
- Troponin is the most specific and sensitive marker for heart damage, typically rising within 3-4 hours after heart injury, peaking at 24-48 hours, and remaining elevated for 7-14 days 1.
- CK-MB rises within 4-6 hours, peaks at 24 hours, and returns to normal within 2-3 days.
- Myoglobin rises earliest (1-3 hours) but is less specific as it can also increase with skeletal muscle damage.
Clinical Use
Elevated cardiac enzymes generally indicate heart damage, but the pattern and timing of elevation help determine whether the damage is from a recent heart attack, ongoing heart damage, or another condition affecting the heart. These tests are typically ordered when a patient presents with chest pain or other symptoms suggesting a heart attack, and are often measured in a series over time to track the progression of heart damage 1.
Recommendations
- Measure cardiac-specific troponin (troponin I or T) at presentation and 3–6 h after symptom onset in all patients with suspected ACS to identify pattern of values 1.
- Obtain additional troponin levels beyond 6 h in patients with initial normal serial troponins with electrocardiographic changes and/or intermediate/high risk clinical features 1.
- Consider time of presentation the time of onset with ambiguous symptom onset for assessing troponin values 1.
- With contemporary troponin assays, CK-MB and myoglobin are not useful for diagnosis of ACS 1.
- High-sensitivity cardiac troponin assays are recommended over less sensitive ones 1.
From the Research
Cardiac Enzymes
Cardiac enzymes, also known as biomarkers, are proteins that are released into the bloodstream when the heart is damaged, such as during a heart attack. The most common cardiac enzymes used to diagnose heart attacks are:
- Creatine Kinase (CK)
- Creatine Kinase isoenzyme MB (CKMB)
- Lactate dehydrogenase (LDH)
- Troponin T (cTnT)
- Troponin I (cTnI)
- Myoglobin
What do Cardiac Enzymes Mean
These enzymes are measured in the blood to help diagnose and manage heart conditions. Elevated levels of these enzymes can indicate:
- Heart attack (myocardial infarction)
- Heart damage or injury
- Unstable angina
- Cardiac arrhythmias
- Heart failure Studies have shown that cardiac troponin T and I are highly sensitive and specific for heart damage, and are often used as the primary biomarkers for diagnosing heart attacks 2, 3, 4, 5, 6.
Interpretation of Cardiac Enzymes
The interpretation of cardiac enzymes depends on the specific enzyme, the level of elevation, and the clinical context. For example:
- Troponin T and I are highly sensitive for heart damage, but may not be elevated in all cases of heart attack
- CKMB is also sensitive for heart damage, but may be elevated in other conditions, such as skeletal muscle injury
- Myoglobin is a sensitive marker for heart damage, but may not be specific for heart attack
- LDH is a less sensitive marker for heart damage, but may be elevated in other conditions, such as liver or skeletal muscle injury
Clinical Use of Cardiac Enzymes
Cardiac enzymes are used in clinical practice to:
- Diagnose heart attacks and other heart conditions
- Monitor the effectiveness of treatment
- Predict outcomes and prognosis
- Guide management decisions, such as the need for further testing or intervention Studies have shown that the use of cardiac enzymes, particularly troponin T and I, can improve the diagnosis and management of heart attacks, and reduce mortality and morbidity 2, 3, 4, 5, 6.