What laboratory finding is characteristic of cholestatic liver disease?

In cholestatic liver disease, the hallmark laboratory finding is an increased alkaline phosphatase level. This increase is due to the obstruction of bile flow within the liver or bile ducts, often as a result of conditions like primary biliary cholangitis, primary sclerosing cholangitis, or bile duct obstruction from gallstones or tumors. Alkaline phosphatase is an enzyme produced by the cells lining the bile ducts, and elevated levels indicate cholestasis or bile duct injury.

While both increased transaminases and high bilirubin levels can be present in cholestatic liver disease, they are not as specific to the condition as increased alkaline phosphatase. Transaminases are more commonly elevated in hepatocellular injury, and while bilirubin levels can rise due to disrupted bile flow, it is the alkaline phosphatase elevation that is most directly associated with cholestatic processes. Decreased alkaline phosphatase would not be characteristic of cholestasis, as it would indicate a lack of bile duct injury or obstruction. Thus, the most indicative and characteristic laboratory finding in cholestatic liver disease is indeed increased alkaline phosphatase.