A 22-year-old man with progressive proximal muscle weakness has serum AST 180 U/L, ALT 160 U/L, and markedly elevated aldolase. His GGT and ALP are normal. Which enzyme finding would BEST confirm that the transaminase elevation arises from skeletal muscle rather than liver?

• A Elevated gamma-glutamyl transferase
• B AST:ALT ratio greater than 2
• C Markedly elevated creatine kinase with a normal GGT ✓
• D Isolated elevation of ALT above AST

Explanation

Skeletal muscle injury releases creatine kinase far out of proportion to any hepatic release, and a normal GGT excludes concurrent hepatobiliary pathology. Aldolase is enriched in skeletal muscle and supports myogenic origin. An AST:ALT ratio above 2 is misleading here because it classically suggests alcoholic liver disease yet also occurs in rhabdomyolysis, since muscle contains abundant AST. The decisive discriminating enzyme is therefore CK measured alongside a normal GGT.

Reference: Harrison's Principles of Internal Medicine, 21st ed.

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Written and medically reviewed by the StethoPrep medical team.