Heart Enzymes: What Are They and When Do They Increase?

What Are Cardiac Enzymes?

Cardiac enzymes are proteins found in the heart muscle and are released into the bloodstream when heart cells are damaged or injured. Their levels in the blood rise in response to this damage. One of the main causes of elevated cardiac enzymes is a heart attack, although other conditions can also lead to an increase. ¹

It is important to note that cardiac enzyme testing primarily relies on Troponin, which is considered the most sensitive and accurate biomarker for detecting heart muscle damage. Other enzymes, such as Creatine kinase (CK), were previously used, but their significance has diminished with the improved accuracy of troponin testing. ¹

Types of Cardiac Enzymes

There are two main types of cardiac enzymes:

• Troponin (Troponin):

This is the most accurate and widely used test to detect heart muscle damage caused by a heart attack. Troponin is highly sensitive to heart muscle injury and starts to rise within 3 to 12 hours after damage occurs, making it an essential early diagnostic tool for heart attacks. ²

• Creatine Kinase (Creatine kinase or CPK):

This enzyme is present in both the heart muscle and other body muscles. Its levels rise in the blood 4 to 6 hours after heart muscle damage and peak at around 24 hours. Elevated levels may indicate a possible heart attack, but they can also rise due to non-cardiac conditions. While troponin is more accurate, some doctors may still check creatine kinase levels as part of heart attack testing. ³

When Do You Need a Cardiac Enzyme Test?

• Diagnosing a Heart Attack: The most common reason for cardiac enzyme testing is to diagnose or rule out a heart attack. Doctors request this test (along with an ECG) in emergency departments when a heart attack is suspected. ²

• Monitoring Treatment (Medications or Surgery): Troponin levels can be tracked to assess the heart's response to medications or surgical treatment.

• Diagnosing Other Heart Conditions: Such as angina or ischemia (restricted blood flow to the heart). ⁴

How Is a Cardiac Enzyme Test Done?

Cardiac enzyme levels are measured through a simple blood test, which is quick and easy and helps detect severe heart conditions early, allowing for immediate treatment and potentially saving lives. ²

Typically, troponin is measured, as it rises in the blood within 3 to 12 hours, peaks in 24-48 hours, and gradually returns to normal levels within 5 to 14 days. Most hospitals conduct the first troponin test upon arrival, followed by another test 4 to 6 hours after symptom onset, and a third test at 12 hours if necessary. The second test helps determine whether troponin or creatine kinase levels follow the typical rise-and-fall pattern seen in heart attacks. ²

• Test Results:

Troponin levels correlate directly with the extent of heart muscle damage—the higher the level, the greater the potential heart damage. However, results must be interpreted carefully by a doctor, as other factors—such as pre-existing conditions or medications—can affect the outcome. ²

A comprehensive diagnosis relies on cardiac enzyme tests, observed symptoms, and an ECG to ensure an accurate assessment of the condition. ²

References

• ¹ BHF - What is troponin?
• ² Patient - Cardiac enzymes
• ³ Verywell Health - Cardiac Biomarkers, Cardiac Enzymes, and Heart Disease
• ⁴ Cleveland Clinic - Cardiac Enzymes (Cardiac Biomarkers)