BOC Clinical Chemistry Practice Test

Elevations of alkaline phosphatase (ALP) and gamma-glutamyl transferase (GGT) together point to a hepatobiliary source for the ALP rise, not bone. ALP has isoenzymes from liver and bone, but GGT is produced in the liver and bile ducts and is not elevated in bone disease. When a patient has ALP about three times the upper limit of normal with a marked rise in GGT, it indicates cholestasis or biliary obstruction, where bile flow is impaired. In obstructive jaundice, the bile ducts are blocked, leading to increased synthesis and release of ALP from the liver and biliary epithelium, along with a pronounced GGT elevation from the same hepatobiliary origin. Conversely, bone diseases can raise ALP without elevating GGT, and hepatocellular hepatitis can raise ALP but typically without the same pattern of a marked GGT rise driven by biliary obstruction. Thus this enzyme pattern best fits obstructive jaundice.