Which enzyme is commonly measured as part of liver function tests?

• A. ALT
• B. AST
• C. BUN
• D. GFR

Answer: (A)

When evaluating liver health, we look for enzymes that leak into the blood when liver cells are damaged. The enzyme that is most commonly measured as a liver-specific marker is alanine aminotransferase (ALT) because it is highly concentrated in hepatocytes and rises predominantly with hepatocellular injury. Elevated ALT points to liver cell damage from conditions like hepatitis, fatty liver disease, or drug-induced injury. In contrast, while aspartate aminotransferase (AST) is also present in the liver, it is found in other tissues such as heart and muscle, making it less specific for liver injury. The other options—BUN and GFR—reflect kidney function, not liver enzymes. So ALT is the best early indicator of hepatocellular damage in standard liver function testing.