A 28-year-old man with acute viral hepatitis A had a peak ALT of 2400 U/L and AST of 1800 U/L at presentation. Five days later, repeat testing shows both enzymes falling. Which statement about their subsequent course is CORRECT?
- A AST will normalize before ALT because AST has a shorter plasma half-life of approximately 17 hours versus about 47 hours for ALT ✓
- B ALT will normalize before AST because ALT has the shorter plasma half-life
- C Both enzymes decline in parallel because they share identical clearance mechanisms
- D AST will remain elevated for weeks because it is bound to albumin
Correct answer: A. AST will normalize before ALT because AST has a shorter plasma half-life of approximately 17 hours versus about 47 hours for ALT
Explanation
The plasma half-life of AST is roughly 17 hours while that of ALT is approximately 47 hours, so AST falls and normalizes earlier even when initial values were lower. This kinetic difference explains why a persistently disproportionate AST late in the course suggests ongoing injury such as alcohol use rather than resolving hepatitis. The distractors invert the half-lives or invoke nonexistent binding behavior; neither transaminase is albumin-bound.
Reference: Harrison's Principles of Internal Medicine, 21st ed.
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