A 52-year-old man with cirrhosis presents with jaundice. Laboratory tests show: serum bilirubin 5.2 mg/dL (direct 4.1 mg/dL), ALP 110 U/L, ALT 68 U/L, albumin 2.8 g/dL, INR 1.8. Ultrasound shows cirrhotic liver with patent portal vein. A 35-year-old woman with painless progressive jaundice for 3 weeks presents with: serum bilirubin 8.4 mg/dL (direct 7.9 mg/dL), ALP 420 U/L, ALT 95 U/L, albumin 3.8 g/dL, INR 1.0. Ultrasound shows dilated intrahepatic and extrahepatic bile ducts with a mass at the pancreatic head. Which single finding best distinguishes intrahepatic cholestasis (cirrhosis) from extrahepatic obstruction (pancreatic cancer)?