A patient admitted with acute MI develops recurrent chest pain 36 hours later. Current troponin T is still elevated from the first event. Which marker is MOST useful to confirm a new infarct at this time?

• A Total LDH with LDH1/LDH2 ratio
• B Repeat troponin T, because it clears faster than CK-MB
• C Myoglobin, because it remains elevated for a week
• D Serial CK-MB, because it returns to baseline within 48 to 72 hours ✓

Explanation

CK-MB has a short plasma half-life and normalizes within roughly 48 to 72 hours after infarction, so a fresh rise above the falling curve signals reinfarction. Cardiac troponins remain elevated for 7 to 14 days, so they cannot distinguish old from new injury during this window. Myoglobin rises and falls within 12 to 24 hours but lacks cardiac specificity, and LDH is obsolete for this purpose.

Reference: Harper's Illustrated Biochemistry, 31st ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.