A 58-year-old man presents 10 hours after onset of chest pain. Serum troponin I is markedly elevated. His total CK is 850 U/L (normal <200), and CK-MB is 170 U/L. What percentage of CK-MB to total CK confirms myocardial infarction?

• A Greater than 3%
• B Greater than 10%
• C Greater than 15%
• D Greater than 6% ✓

Explanation

A CK-MB fraction exceeding 6% of total CK indicates myocardial origin rather than skeletal muscle injury, where CK-MB may rise in absolute terms but rarely exceeds 6% of total CK. In this patient CK-MB/total CK = 170/850 = 20%, confirming myocardial infarction. CK-MB percentage thresholds below 6% are consistent with skeletal muscle disease.

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

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.