Why is alanine aminotransferase (ALT) considered more specific than aspartate aminotransferase (AST) for hepatocellular damage?
- A ALT is found almost exclusively in the cytoplasm of hepatocytes, while AST is abundant in heart, skeletal muscle, kidney, and brain ✓
- B ALT has a longer plasma half-life than AST
- C ALT is released only after mitochondrial rupture
- D ALT is cleared exclusively by the liver
Correct answer: A. ALT is found almost exclusively in the cytoplasm of hepatocytes, while AST is abundant in heart, skeletal muscle, kidney, and brain
Explanation
ALT is localised almost entirely to the cytosol of hepatocytes, so a raised ALT points strongly to liver cell injury. AST, in contrast, is distributed widely in heart, skeletal muscle, kidney, brain, and liver, and exists in both cytosolic and mitochondrial forms, so it rises in myocardial infarction, myositis, and haemolysis as well. Distribution, not half-life or clearance route, is what confers the superior specificity of ALT for hepatic injury.
Reference: Harper's Illustrated Biochemistry, 31st ed.
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