Which biomarker is the earliest enzyme elevated in acute myocardial infarction?

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

Answer: (A)

In acute myocardial infarction, heart cell injury releases substances into the blood in a characteristic sequence. Among enzymatic markers, CK-MB is the first to rise. CK-MB is an enzyme present mainly in cardiac muscle, so when cardiac cells are damaged it leaks into the bloodstream within about 3–6 hours, peaks around 24 hours, and returns to baseline in a couple of days.

Troponin I, while highly specific for cardiac injury, is not an enzyme and tends to rise a bit later than CK-MB, staying elevated for a longer period. LDH is another enzyme that rises but later than CK-MB. Myoglobin appears even earlier than CK-MB, but it is not an enzyme, and its lack of specificity makes it less ideal as a sole cardiac marker.

Thus, CK-MB is the earliest enzyme elevated in this setting.