A 58-year-old man presents with crushing chest pain 6 hours ago. Serial cardiac enzymes are ordered. Which isoenzyme pattern on serum electrophoresis is MOST specific for myocardial infarction?

• A CK-BB elevation
• B CK-MM with total CK >1000 U/L
• C LDH-1 alone elevation
• D CK-MB >6% of total CK with CK-MB mass >10 ng/mL ✓

Explanation

CK-MB isoenzyme constitutes <5% of skeletal muscle CK but >25% of myocardial CK; a relative index >6% (CK-MB/total CK ×100) combined with absolute mass >10 ng/mL provides high specificity for myocardial injury. CK-BB is brain-specific and CK-MM is predominantly skeletal. LDH-1 flip (LDH-1 > LDH-2) supports MI but CK-MB is the standard enzyme index.

Reference: Harper's Illustrated Biochemistry, 32nd ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

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