Which analyte has the highest specificity for cardiac injury?

Which analyte has the highest specificity for cardiac injury?

• A. TnI
• B. CK-MB mass assays
• C. Total CK-MB
• D. AST

Answer: (A)

Troponin I is the most specific indicator of myocardial injury because it has a cardiac-specific isoform that is not expressed in appreciable amounts in skeletal muscle or other tissues. When heart muscle is damaged, troponin I is released into the blood and remains elevated for an extended period, giving a clear signal of cardiac injury with minimal confounding from non-cardiac sources. CK-MB is more specific to cardiac tissue than AST or total CK, but it can also rise with skeletal muscle injury, reducing its specificity. AST is a broad marker that appears in liver, heart, and skeletal muscle, so its elevation is not specific to the heart. Therefore, the analyte with the highest cardiac specificity is troponin I.

Troponin I is the most specific indicator of myocardial injury because it has a cardiac-specific isoform that is not expressed in appreciable amounts in skeletal muscle or other tissues. When heart muscle is damaged, troponin I is released into the blood and remains elevated for an extended period, giving a clear signal of cardiac injury with minimal confounding from non-cardiac sources.

CK-MB is more specific to cardiac tissue than AST or total CK, but it can also rise with skeletal muscle injury, reducing its specificity. AST is a broad marker that appears in liver, heart, and skeletal muscle, so its elevation is not specific to the heart. Therefore, the analyte with the highest cardiac specificity is troponin I.