In an acute myocardial infarction, which sequence correctly lists the first to last appearance of elevated enzymes: AST, CK, and LD?

• A. AST, LD, CK
• B. CK, LD, AST
• C. CK, AST, LD
• D. LD, CK, AST

Answer: (C)

In myocardial infarction, enzymes rise in a predictable order because of where they are inside heart muscle cells and how quickly they leak out after injury. CK, especially the CK-MB isoenzyme specialized for heart muscle, is released first. It appears in the blood within about 4–6 hours after onset of chest pain and tends to peak around 12–24 hours, then falls back toward normal over a couple of days. Next comes AST, which is abundant in heart and also in liver and skeletal muscle; it rises a bit later, typically 8–12 hours after onset, with a peak around 24–48 hours. LD then rises last, as it is present in many tissues and leaks more slowly, usually elevating around 24–48 hours and peaking at 2–3 days or so before slowly declining. Therefore, the sequence CK (earliest) → AST → LD (latest) best matches the typical pattern observed in MI. In modern practice, troponin assays are preferred for their higher specificity, but this enzyme timeline is a classic teaching point.