14.1 : Blood Studies for Cardiovascular System I: Cardiac Biomarkers

Cardiac biomarkers are enzymes, proteins, and hormones released into the blood when cardiac cells are injured. They are powerful tools for triaging.

The essential diagnostic tools for detecting myocardial necrosis and monitoring individuals suspected of having acute coronary syndrome (ACS) include:

Troponins

Troponins, particularly cardiac troponins I and T, are the most precise and sensitive markers of myocardial injury. They are detectable within 4-6 hours of myocardial injury and remain elevated for 10-14 days. High-sensitivity troponin assays have revolutionized the timely detection of ACS, allowing for earlier intervention and improved patient outcomes. Elevated troponin levels are definitive indicators of myocardial infarction, guiding immediate therapeutic interventions and informing prognosis.

Myoglobin

Myoglobin, an oxygen-binding protein, is released early after myocardial injury, often within 1 to 3 hours. It reaches peak concentrations at 12 hours and returns to baseline quickly. The early release of myoglobin makes it a crucial marker for rapidly identifying myocardial injury, although its specificity is lower than that of other biomarkers.

Creatine Kinase-MB (CK-MB)

Creatine kinase-MB (CK-MB), a subtype of creatine kinase, is released during myocardial infarction (MI). CK-MB levels rise rapidly, peaking within 12 to 24 hours post-infarction and normalizing within 48 hours. The quick rise and fall of CK-MB levels make them particularly useful in detecting reinfarction, offering a temporal marker for recurring myocardial injury.

Clinical Significance of Cardiac Biomarkers

Myocardial cells that become necrotic from prolonged ischemia or trauma release specific enzymes (creatine kinase [CK]), CK isoenzymes (CK-MB), and proteins (myoglobin, troponin T, and troponin I). These substances leak into the interstitial spaces of the myocardium and are carried by the lymphatic system into general circulation. As a result, abnormally high levels of these substances can be detected in serum blood samples, aiding in diagnosing and managing myocardial injury and ACS.