When cells are injured or die, their intracellular enzymes leak into the bloodstream. Measuring these enzyme levels helps identify which organ has been damaged.
Key Serum Enzymes and Associated Tissue Injury
| Enzyme Marker | Main Source / Tissue | Clinical Significance | Example Conditions |
|---|---|---|---|
| AST (Aspartate Aminotransferase) | Liver, cardiac muscle, skeletal muscle | Indicates liver injury (also rises in heart and muscle damage) | Hepatitis, myocardial infarction, and muscle injury |
| ALT (Alanine Aminotransferase) | Liver (more specific than AST) | Marker of hepatocellular injury | Viral hepatitis, drug-induced liver injury |
| CK-MB (Creatine Kinase – MB Isoenzyme) | Cardiac muscle | Marker of heart injury | Myocardial infarction |
| Amylase | Pancreas, salivary glands | Marker of pancreatic injury and salivary gland damage | Acute pancreatitis, mumps |
| Lipase | Pancreas | More specific marker for pancreatic injury | Acute pancreatitis |
Key Points to Remember
- Enzymes are released into the blood when cell membranes are damaged.
- ALT > AST suggests liver-specific injury (e.g., viral hepatitis).
- AST > ALT may occur in alcoholic liver disease or muscle injury.
- CK-MB rises earlier and returns to normal faster than troponin in myocardial infarction.
- Lipase remains elevated longer than amylase in pancreatitis.
Learning Objective
After studying this topic, students should be able to: Identify major serum enzyme markers of cell injury and correlate specific enzyme elevations with damage to the liver, heart, pancreas, and other tissues.
