CK isoenzyme fractionation showing two peaks, CK-MM and CK-MB, may indicate which condition?

• A. Brain tumor
• B. Muscular dystrophy
• C. Myocardial infarction
• D. Viral hepatitis

Answer: (C)

The key idea is that CK exists in three tissue-specific forms, and identifying which one is elevated helps pinpoint the source of muscle injury. CK-MM comes mainly from skeletal muscle, CK-MB is the cardiac isoenzyme, and CK-BB comes from brain tissue. When cardiac muscle is damaged, as in a myocardial infarction, CK-MB is released into the bloodstream and rises, often alongside CK-MM if there is concurrent skeletal muscle involvement or baseline leakage. Seeing a pattern that includes an elevated CK-MB peak is a strong indicator of heart muscle injury and points to myocardial infarction rather than skeletal muscle disease or liver/brain conditions. Thus, this isoenzyme pattern best fits myocardial infarction.