Which biomarker remains elevated longest after myocardial infarction?

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

Answer: (C)

Troponin stays elevated the longest after a myocardial infarction because it is released from dying cardiac myocytes and remains in the blood for an extended period. Cardiac troponins I and T are highly specific for heart tissue. After injury, they rise within a few hours and stay elevated for about 7–10 days (troponin I) to up to about two weeks (troponin T). In contrast, CK-MB levels rise with necrosis but usually normalize within 2–3 days, myoglobin rises very early but clears within about 24 hours, and AST is less specific and returns to baseline within several days. Therefore, troponin remains elevated the longest, making it the most durable marker for diagnosing MI days after onset.