A 62-year-old man was admitted 6 days ago with an anterior STEMI treated by primary PCI. Today his chest pain has returned. Cardiac enzymes are ordered to evaluate for reinfarction. Which biomarker is most appropriate to distinguish new myocardial necrosis from the index infarction at this time point?
- A Cardiac troponin I
- B Cardiac troponin T
- C CK-MB fraction ✓
- D Lactate dehydrogenase
Correct answer: C. CK-MB fraction
Explanation
CK-MB rises within 4 hours, peaks around 24 hours, and returns to baseline by 48 to 72 hours, so any rise on day 6 indicates fresh necrosis. Troponins I and T remain elevated for 7 to 14 days after an infarct, making them useless for diagnosing reinfarction during this window. LDH peaks late and is nonspecific; it is obsolete for this purpose.
Reference: Harrison's Principles of Internal Medicine, 21st ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.