Fernando De Ritis noticed in 1957 that the balance between two liver enzymes shifts with the type of liver injury. Dividing AST by ALT still helps separate fatty liver and viral patterns from alcoholic and cirrhotic ones.
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Two enzymes, two addresses
ALT lives almost entirely inside liver cells, so its rise points squarely at the liver. AST is more cosmopolitan, abundant in heart, skeletal muscle, kidney, and red blood cells as well as liver. When liver injury releases both, the ratio between them carries information about the cause. Fernando De Ritis described this in 1957, and the ratio still bears his name in clinics around the world.
What each pattern suggests
Most liver conditions push ALT higher than AST, giving a ratio under one. Viral hepatitis and nonalcoholic fatty liver disease classically follow this pattern. Alcoholic liver disease flips it, because alcohol depletes the vitamin B6 that ALT production needs while damaging mitochondria that spill AST. A ratio above two, especially with modest enzyme elevations, raises the possibility of alcoholic hepatitis. Once cirrhosis develops from any cause, fibrosis slows ALT clearance and the ratio drifts above one even in originally ALT dominant diseases.
The muscle exception
Strenuous exercise, muscle injury, and statin related muscle complaints release AST with little ALT, bending the ratio upward without any liver problem at all. When the story does not fit, checking creatine kinase separates muscle from liver in one extra tube of blood.
A supporting actor, never the lead
The ratio refines a picture that enzymes alone start, and it earns its keep most when combined with the clinical story and tools like FIB-4. It performs poorly as a lone screening test in people with normal enzymes. Used wisely after an abnormal panel though, this simple division from 1957 still shortens the diagnostic path.