A 58-year-old man presents 12 hours after onset of severe chest pain. Serum troponin I is markedly elevated. Regarding cardiac troponin I (cTnI), which statement best describes its diagnostic superiority over CK-MB?
- A cTnI rises faster within 1–2 hours of myocardial injury compared to 4–6 hours for CK-MB
- B cTnI is elevated in skeletal muscle injury, giving fewer false positives than CK-MB
- C cTnI remains elevated for 7–10 days, enabling detection of MI presenting late, while CK-MB normalises by 48–72 hours ✓
- D cTnI is a better marker of reinfarction because it re-elevates after returning to baseline within 24 hours
Correct answer: C. cTnI remains elevated for 7–10 days, enabling detection of MI presenting late, while CK-MB normalises by 48–72 hours
Explanation
Cardiac troponin I (cTnI) is expressed exclusively in cardiac muscle and remains elevated for 7–10 days after myocardial infarction, making it ideal for late-presenting patients. CK-MB normalises within 48–72 hours. CK-MB (not troponin) is preferred for detecting reinfarction due to its shorter window. Both markers rise at approximately 4–6 hours post-infarction.
Reference: Harper's Illustrated Biochemistry, 32nd ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
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