A 58-year-old man presents 18 hours after onset of crushing chest pain. Serum troponin I is elevated, but CK-MB has already returned to normal. Which property of troponin I makes it superior to CK-MB for detecting myocardial infarction in this time window?
- A Troponin I remains elevated for 7–10 days while CK-MB normalizes within 48–72 hours ✓
- B Troponin I has a shorter half-life than CK-MB
- C Troponin I is released faster into circulation than CK-MB
- D Troponin I has higher molecular weight enabling faster renal clearance
Correct answer: A. Troponin I remains elevated for 7–10 days while CK-MB normalizes within 48–72 hours
Explanation
Cardiac troponin I (cTnI) is released from damaged cardiomyocytes and remains elevated for 7–10 days, making it the preferred marker for late-presenting myocardial infarction (the 'prolonged window'). CK-MB peaks at 12–24 hours and normalizes by 48–72 hours. Troponin I's sustained elevation is due to its slow release from the structural contractile apparatus after initial soluble-pool release. Options A and D are incorrect; its higher sensitivity and specificity at late presentation stems from prolonged elevation, not faster clearance.
Reference: Harper's Illustrated Biochemistry, 32nd ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.