Which biomarker is most specific for myocardial necrosis?

• A. CK-MB
• B. Myoglobin
• C. Troponin I
• D. AST

Answer: (C)

Troponin I stands out because it is highly specific to cardiac muscle. When heart muscle is damaged, cardiac troponin I is released into the bloodstream in a way that is much less likely to occur with injury to skeletal muscle or other tissues. This cardiac-specific isoform allows clinicians to diagnose myocardial injury with high accuracy, especially when measured with modern, highly sensitive immunoassays.

In addition to its specificity, troponin I remains elevated for an extended period after injury, providing a reliable window for detection even if the event occurred hours to days earlier. Other markers, like CK-MB, can rise with non-cardiac muscle injury and are less specific for the heart; myoglobin rises very early but lacks specificity, and AST is even less specific because it is present in liver and skeletal muscle as well.