Serum liver function indicators include alanine aminotransferase, glutamine aminotransferase, and lactate dehydrogenase isoenzymes, but total bilirubin and direct bilirubin are more reflective of the state of liver function, while alkaline phosphatase and glutamyltransferase reflect the presence or absence of extrahepatic bile duct obstruction. If alkaline phosphatase, glutamyl transpeptidase and direct bilirubin are significantly elevated, extrahepatic bile duct obstruction and gallstones are considered, and a definitive diagnosis can be made by liver ultrasound or CT of the upper abdomen. Liver cell damage is also considered in patients with cirrhosis. In patients with cirrhosis, blood ammonia is also checked to determine the presence of hepatic encephalopathy.