Which biomarker is most specific for myocardial infarction?

• A. CK-MB
• B. Myoglobin
• C. BNP
• D. Cardiac troponin I or T

Answer: (D)

Cardiac troponins I and T are the most specific indicators of myocardial injury. These proteins are found only in heart muscle, so when a myocardial infarction damages cardiac cells, troponins are released into the bloodstream. Their heart-specific nature means their presence in the blood strongly points to cardiac injury, and they remain elevated for a prolonged period, aiding diagnosis and monitoring.

CK-MB rises with heart damage but is less specific because it can also come from skeletal muscle and other conditions, making it a less reliable sole indicator of MI. Myoglobin appears quickly after injury but is not heart-specific, so it can be elevated from non-cardiac sources. BNP reflects ventricular stretch and is used mainly to assess heart failure, not acute MI. Thus, the most specific biomarker for MI is cardiac troponin I or T.