Cardiac markers are substances released into the bloodstream that signal damage or stress to the heart muscle. These indicators are typically proteins or enzymes that become detectable when heart tissue is compromised. Measuring their concentration in a blood sample provides immediate, objective information about a patient’s cardiac status. They are essential in emergency settings for the rapid assessment of individuals experiencing symptoms like chest pain or shortness of breath.
What Cardiac Markers Are and Why They Are Measured
These biological substances are normally stored within the cells of the heart muscle. When the heart experiences injury, such as from ischemia—a lack of oxygenated blood flow—the integrity of the cell walls is compromised. This cellular damage causes the internal components to leak out into the surrounding fluid.
The markers then enter the peripheral blood circulation, where they can be detected using a blood test. The amount of marker measured directly correlates with the extent of the myocardial damage. Measuring these released substances helps clinicians determine if a cardiac event has taken place and assess the severity of the injury.
Key Markers Used for Acute Heart Injury
Cardiac Troponin (cTn) is the primary marker used for detecting acute heart injury, such as a heart attack. Troponin is a complex of three proteins—Troponin I, T, and C—that regulate muscle contraction. The cardiac-specific isoforms, Troponin I (cTnI) and Troponin T (cTnT), are highly sensitive and specific to heart muscle tissue.
When a heart attack occurs, troponin is released into the blood, often becoming detectable within a few hours of symptom onset. High-sensitivity troponin assays have significantly improved the speed and accuracy of diagnosis by detecting even minute concentrations. These assays allow for earlier detection and a more rapid rule-in or rule-out of an acute coronary event.
Historically, Creatine Kinase (CK) and its heart-specific isoform, Creatine Kinase-MB (CK-MB), were used. CK-MB is more concentrated in the heart than in skeletal muscle, but it is not as specific as troponin. While troponin has largely replaced CK-MB for initial diagnosis, CK-MB may still be used to look for evidence of a re-infarction. This is because CK-MB levels return to normal faster than troponin, making its re-elevation a clearer sign of a new injury shortly after the first event.
Markers for Heart Failure and Cardiovascular Risk
Other markers assess chronic conditions and long-term risk, rather than acute injury. B-type Natriuretic Peptide (BNP) and N-terminal pro-BNP (NT-proBNP) are proteins used for the diagnosis and prognosis of heart failure. These markers are distinct from troponin because they are released not due to cell death, but in response to the stretching of the heart’s ventricles.
When the heart struggles to pump effectively, pressure and volume increase, causing the ventricular walls to stretch. This stretching stimulates the release of BNP and its precursor, NT-proBNP, into the circulation. Elevated levels help clinicians confirm a diagnosis of heart failure when symptoms like shortness of breath are present, and provide insight into the severity of the condition.
High-Sensitivity C-Reactive Protein (hs-CRP)
High-sensitivity C-Reactive Protein (hs-CRP) is a general marker of inflammation throughout the body. While not specific to the heart, chronic systemic inflammation contributes to the development of atherosclerosis, which hardens and narrows the arteries. An elevated hs-CRP level suggests a heightened cardiovascular risk, even without acute symptoms. This information helps guide preventative treatment strategies to lower a patient’s overall risk profile.
Understanding the Testing and Interpretation Process
A single cardiac marker measurement is often insufficient for a definitive diagnosis of an acute event. Because markers like troponin take time to leak into the bloodstream after an injury, a strategy called “serial testing” is employed. This involves taking multiple blood samples over a period of several hours to track the marker’s level.
For patients with suspected heart attacks, blood is typically drawn upon arrival and then again at intervals, such as three or six hours later. A positive result is not just a single elevated reading, but a distinct pattern of a rise and/or fall in the marker concentration over these serial tests. This dynamic change indicates a recent, active injury to the heart muscle.
The final interpretation integrates the marker levels with the patient’s symptoms and findings from an electrocardiogram (EKG). The EKG shows the heart’s electrical activity, while the markers show the biochemical evidence of damage. Only by combining these pieces of information can a definitive diagnosis be established.