When evaluating a markedly elevated alkaline phosphatase, which enzyme helps distinguish hepatobiliary disease from bone pathology?

• A. Gamma-glutamyl transferase
• B. Liver function tests
• C. Bilirubin levels
• D. Carcinoembryonic antigen

Answer: (A)

Elevated alkaline phosphatase can come from bone or from the liver/biliary tract, so you need a marker that specifically points to hepatobiliary origin. Gamma-glutamyl transferase rises with hepatobiliary disease and remains normal in pure bone disease, making it the best discriminator when ALP is high. So a high GGT alongside elevated ALP strongly suggests a liver/biliary source, whereas a high ALP with a normal GGT points toward bone activity. Bilirubin levels can be elevated with biliary obstruction or liver dysfunction but don’t tell you whether the ALP is coming from bone or liver. Liver function tests cover multiple enzymes but don’t isolate the source of ALP, and a tumor marker like carcinoembryonic antigen isn’t relevant to distinguishing bone from liver disease.