Which enzyme marker is most commonly used to indicate hepatobiliary obstruction?

• A. Alkaline Phosphatase
• B. AST
• C. ALT
• D. Ammonia

Answer: (A)

When bile flow is blocked (cholestasis), alkaline phosphatase rises prominently because it is abundant in bile duct cells and is released into the blood when bile formation or flow is impeded. This makes it the most sensitive and commonly used marker for hepatobiliary obstruction. In contrast, AST and ALT reflect hepatocellular injury rather than obstruction, so they’re not as specific for biliary blockage. Ammonia rises with severe liver dysfunction and encephalopathy, not simply with obstruction. (Note: ALP can also come from bone, so clinicians sometimes use a hepatic-specific marker like GGT to confirm the liver origin, but ALP remains the primary indicator of hepatobiliary obstruction.)