Cardiac Markers: A Guide to Heart-Related Blood Tests

Key takeaways

• Cardiac markers are proteins or enzymes released into the blood when heart muscle is injured or stressed.
• Troponin is the preferred marker for detecting heart muscle injury because it is highly specific to the heart.
• Other markers such as CK-MB, myoglobin, and BNP or NT-proBNP serve different roles, from detecting muscle injury to assessing heart failure.
• Cardiac marker results are interpreted alongside symptoms, physical exam, ECG findings, and imaging, not in isolation.
• Marker levels can rise for reasons other than a heart attack, so abnormal results always require clinical context.

What Are Cardiac Markers?

Cardiac markers are biological substances that enter the bloodstream when the heart muscle is damaged, strained, or under stress. Under normal circumstances, many of these proteins and enzymes are found mostly inside heart muscle cells or are present at low levels in blood. When cells are injured, their contents leak into circulation, where a blood test can detect them.

Doctors use cardiac marker tests most often in emergency settings when someone has chest pain, shortness of breath, or other symptoms that could indicate a heart attack. They are also used to monitor known heart conditions, assess heart failure, and sometimes to evaluate the effects of treatments or procedures on the heart.

Commonly Measured Cardiac Markers

Troponin is the most widely used and most specific cardiac marker. Troponin I and troponin T are proteins that regulate muscle contraction, and the cardiac forms are found almost exclusively in heart muscle. When heart muscle is injured, troponin levels rise within a few hours and can remain elevated for days, which makes it useful for both early detection and later confirmation of injury.

Creatine kinase-MB (CK-MB) is an enzyme found in heart muscle that was once a primary marker for heart attacks. It rises and falls faster than troponin, so it is sometimes used to detect a second injury shortly after an initial event. Myoglobin is another protein that rises very quickly after muscle injury, but because it is also found in skeletal muscle, it is less specific to the heart. B-type natriuretic peptide (BNP) and its precursor NT-proBNP are released when the heart stretches or works under increased pressure, and they are used mainly to evaluate heart failure rather than heart attacks.

How Cardiac Marker Testing Is Done

Cardiac marker testing requires a blood sample, usually drawn from a vein in the arm. In an emergency evaluation for possible heart attack, the sample is often collected shortly after arrival and then repeated several hours later. This serial testing is important because troponin may be normal very early after symptoms begin and rise over time.

Results are typically available within an hour or two in hospital laboratories that offer rapid testing. The exact timing and number of draws depend on the clinical situation, the marker being measured, and the protocols of the treating facility. Some point-of-care tests can provide troponin results even faster in emergency departments.

Interpreting Cardiac Marker Results

A single elevated troponin level does not automatically mean a person has had a heart attack. Troponin can rise in conditions such as myocarditis, heart failure, kidney disease, pulmonary embolism, and extreme physical exertion. Clinicians look at the pattern of change over time, the person's symptoms, ECG results, and imaging to determine whether the elevation reflects an acute heart attack or another cause.

BNP and NT-proBNP levels help distinguish heart failure from other causes of shortness of breath, but they also can be affected by age, kidney function, and other medical conditions. Because of this, reference ranges vary between laboratories, and results should always be interpreted by a qualified healthcare professional in the context of the whole clinical picture.

Frequently Asked Questions

Sources

• MedlinePlus: Troponin Test
• MedlinePlus: Heart Diseases
• National Heart, Lung, and Blood Institute: Heart Attack
• Mayo Clinic: Heart Attack
• Centers for Disease Control and Prevention: Heart Disease