Leucine aminopeptidase, which is generally referred to as LAP in liver function, is a protein enzyme that is widely distributed in all organs of the body and is especially abundant in the liver, and the normal value for leucine aminopeptidase is generally between 1.9 and 3.2 mmol/L. Any patient within this range should be considered to have a normal leucine aminopeptidase. If the patient has elevated leucine aminopeptidase, it is possible that the patient has biliary stasis, intrahepatic bile duct obstruction, especially for some malignant tumor diseases that cause biliary obstruction in patients, the patient’s leucine aminopeptidase will be significantly elevated, the elevation time is earlier than bilirubin and alkaline phosphatase, etc., and the sensitivity is higher. In some cases of liver infection, breast tumor, biliary tract tumor, and uterine tumor, leucine aminopeptidase may be elevated, and the elevated value is about 2-5 times the normal value.