After an acute myocardial infarction, which cardiac biomarker is released first?

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

Answer: (C)

Immediately after myocardial injury, the earliest marker that becomes detectable in the blood is myoglobin. Its small size lets it leak into the bloodstream quickly from damaged muscle cells, so levels rise within about 1 to 3 hours, peaking around 6 to 9 hours, and returning toward baseline within roughly 24 to 36 hours. This makes it the first biomarker to appear after an acute MI, before the other commonly used markers.

BNP is a peptide released in response to ventricular stretch and is more useful for assessing heart failure rather than acute myocardial necrosis. CK-MB rises later, typically 3 to 12 hours after onset, peaks around 24 hours, and returns to baseline within 48 to 72 hours. Cardiac troponins I and T also rise within 3 to 12 hours but remain elevated for days, which is why they’re favored for confirming MI, though they don’t appear first.