Question

Name a commonly used biomarker for early detection of acute myocardial infarction.

• A. Creatine kinase -MM
• B. Creatine kinase -MB
• C. Alkaline phosphatase
• D. Gamma glutamyl transferase

Hint:

While cardiac troponins (I and T) have largely succeeded CK-MB in modern human medicine due to even higher sensitivity, CK-MB remains a highly important and classic exam answer for cardiac-specific enzymology.
Remember: MB stands for Myocardium/Brain, but clinically represents the Heart marker.

Answer 1

The Correct Option is B

Step 1: Understanding the Concept:
Myocardial infarction (heart attack) causes necrosis of cardiac muscle cells, releasing intracellular cardiac enzymes and proteins into the bloodstream.
Measuring these molecules in serum serves as a highly specific diagnostic tool for early detection.

Step 2: Detailed Explanation:
Creatine kinase (CK) is a dimeric enzyme that catalyzes the reversible phosphorylation of creatine using ATP.
It exists as three distinct isoenzymes formed by the association of two different subunits: M (muscle) and B (brain).
1. CK-MM (A): Found predominantly in skeletal muscle.
2. CK-BB: Found primarily in brain tissue.
3. CK-MB (B): This isoenzyme is highly specific to cardiac muscle tissue, where it accounts for about $15\text{--}20\%$ of the total creatine kinase activity (compared to only $1\text{--}2\%$ in skeletal muscle).
When myocardial cells are damaged during an acute myocardial infarction, CK-MB is released rapidly into the bloodstream.
Its serum levels begin to rise within $3\text{--}6$ hours of the onset of chest pain, peak at $18\text{--}24$ hours, and return to baseline within $48\text{--}72$ hours.
Because of this rapid kinetic profile and high cardiac specificity, CK-MB is a classic and widely used diagnostic biomarker for early detection of myocardial infarction.
Alkaline phosphatase (C) and GGT (D) are biomarkers primarily associated with liver and bone disorders, not cardiac injury.

Step 3: Final Answer:
The cardiac-specific biomarker is Creatine kinase-MB, which corresponds to option (B).