The specificity of biochemical markers of cardiac damage: a problem solved

Area of Science:

• Biomarkers of Cardiovascular Disease
• Clinical Chemistry
• Diagnostic Assays

Background:

• Creatine kinase-MB (CK-MB) is a commonly used marker for myocardial infarction but lacks absolute cardiac specificity.
• Skeletal muscle can express CK-MB, leading to potential false positives in diagnosing heart damage.
• Cardiac troponin I (cTnI) and cardiac troponin T (cTnT) are cardiac-specific proteins released into circulation upon myocardial injury.

Purpose of the Study:

• To review the tissue specificity of cTnI, cTnT, and CK-MB in cardiac and skeletal muscles.
• To evaluate the diagnostic utility of cTnI and cTnT as markers of myocardial injury in both human and animal models.
• To highlight the limitations of CK-MB and the advantages of cardiac troponins in clinical diagnostics.

Main Methods:

• Review of existing literature on the expression and specificity of cTnI, cTnT, and CK-MB.
• Analysis of studies examining troponin isoforms in human and animal skeletal and cardiac muscle.
• Case study review demonstrating the differentiation of myocardial injury from skeletal muscle injury using cardiac troponins.

Main Results:

• CK-MB is not 100% specific for the heart, with up to 20% activity found in human skeletal muscle.
• One cTnI isoform is 100% specific for the heart.
• While cTnT isoforms exist in diseased/regenerating skeletal muscle, they differ from cardiac isoforms and are not detected by clinical assays.
• cTnI and cTnT assays demonstrate sufficient reactivity and tissue specificity for detecting myocardial injury in laboratory animals.

Conclusions:

• Cardiac troponins (cTnI and cTnT) are highly specific biomarkers for myocardial injury, offering superior diagnostic accuracy compared to CK-MB.
• Monitoring circulating cTnI and cTnT levels is becoming the standard for detecting heart damage.
• These troponin assays are validated for use in both human clinical practice and animal research settings.