Which markers are predominantly elevated in biliary obstruction?

• A. ALP and Bilirubin
• B. ALT and AST
• C. Ammonia and Bilirubin
• D. GGT and ALT

Answer: (A)

Biliary obstruction causes cholestasis, so substances related to bile flow accumulate in the blood. Alkaline phosphatase comes from bile duct cells, and it rises when bile flow is blocked. Bilirubin also increases because the excretion of conjugated bilirubin into the bile is impaired, letting it back up into the bloodstream. This combination—raised alkaline phosphatase and elevated bilirubin—best reflects a biliary obstruction. In contrast, ALT and AST indicate hepatocellular injury to liver cells rather than a blockage of bile flow, and ammonia elevation points to impaired liver detoxification or hepatic failure rather than obstruction. GGT can be elevated in cholestasis too, but the most characteristic pairing for obstruction is alkaline phosphatase with bilirubin.