Which cardiac marker appears 3-6 hours after MI and remains elevated for 2-4 days and is specific to heart muscle?

Which cardiac marker appears 3-6 hours after MI and remains elevated for 2-4 days and is specific to heart muscle?

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

Answer: (B)

The key idea is how cardiac markers rise and fall after a myocardial injury and what their timing tells us about the event. CK-MB is an enzyme isoform found predominantly in heart muscle that leaks into the blood when heart cells are damaged. It typically becomes detectable about 4–6 hours after the infarct and remains elevated for roughly 2–3 days (often described as up to 2–4 days). This pattern fits the question’s time frame and its relative specificity for myocardial tissue, making it the best choice for indicating myocardial injury within this window. Troponin I or T would also rise in a similar early window (around 3–6 hours), but they stay elevated longer, often 7–10 days, which doesn’t match the 2–4 day duration described. Myoglobin rises very early (1–3 hours) but is not specific to the heart. LDH rises later and is less specific for cardiac injury.

The key idea is how cardiac markers rise and fall after a myocardial injury and what their timing tells us about the event. CK-MB is an enzyme isoform found predominantly in heart muscle that leaks into the blood when heart cells are damaged. It typically becomes detectable about 4–6 hours after the infarct and remains elevated for roughly 2–3 days (often described as up to 2–4 days). This pattern fits the question’s time frame and its relative specificity for myocardial tissue, making it the best choice for indicating myocardial injury within this window.

Troponin I or T would also rise in a similar early window (around 3–6 hours), but they stay elevated longer, often 7–10 days, which doesn’t match the 2–4 day duration described. Myoglobin rises very early (1–3 hours) but is not specific to the heart. LDH rises later and is less specific for cardiac injury.