Bishop Clinical Chemistry Practice Test 2026 – The All-in-One Guide to Mastering Your Exam!

Cholestasis from bile duct obstruction causes a buildup of bile in the liver, and the cells lining the biliary tract release alkaline phosphatase into the bloodstream. Alkaline phosphatase is highly concentrated in bile ducts, so when drainage is blocked, its level rises prominently. This makes it a sensitive indicator of biliary obstruction and hepatobiliary disease.

In contrast, AST and ALT are enzymes released mainly from hepatocytes when there is direct liver cell injury, such as hepatitis or ischemia; their elevations reflect hepatocellular damage rather than obstruction. Ammonia rises when liver function is severely impaired and fails to detoxify, but it is not specific to obstruction and can be elevated in a range of liver dysfunction scenarios.

Thus, alkaline phosphatase is the most useful marker for identifying hepatobiliary disease due to bile duct obstruction, and its elevation is often interpreted alongside markers like GGT to confirm a hepatic (not bone) origin.