Here is an example of intrahepatic ducct obstruction with a small stone present within an intrahepatic bile duct. This could produce a localized cholestasis in the liver, but the serum bilirubin would not be increased, because there is plenty of non-obstructed liver to clear the bilirubin from the blood. However, the serum alkaline phosphatase will be increased with biliary tract obstruction at any level.