Arginase belongs to the urea hydrolase family of enzymes. It's one of the key enzymes in the urea nitrogen cycle and catalyzes the fifth and final step in the urea cycle, a series of biochemical reactions in mammals during which the body disposes of harmful ammonia. Specifically, arginase converts L-arginine into L-ornithine and urea. It was found to be highly specific in normal liver cells, but not in bile duct epithelial cells, hepatic sinus endothelial cells, vascular endothelial cells, and Kupffer cells. It is a specific and sensitive marker for hepatocellular adenoma and hepatocellular carcinoma (more sensitive and specific than HepPar1 and Glypican-3).