Leucine aminopeptidase is a protein enzyme that is measured by blood tests and is used clinically to aid in the diagnosis and differential diagnosis of lesions of the hepatobiliary system. Many clinical liver pathologies can cause elevation of leucine aminopeptidase. Among them, multiple causes of hepatitis and cirrhosis are responsible for high leucine aminopeptidase. In primary hepatocellular carcinoma with biliary obstructive disease, leucine aminopeptidase may be significantly elevated, although it may be only mildly elevated in the early stages of the lesion. Compared to bilirubin and alkaline phosphatase, leucine aminopeptidase is more sensitive and may be elevated early in the course of the lesion, which is better diagnosed with imaging. Leucine aminopeptidase may also be elevated in malignant tumors, such as pancreatic cancer, endometrial cancer, and ovarian cancer. In addition, a mildly elevated leucine aminopeptidase in urine is likely to be associated with kidney disease, such as renal cancer, glomerulonephritis and nephrotic syndrome.