AST (aspartate aminotransferase) is a liver enzyme that occurs inside hepatocytes or liver cells. Normal blood levels of AST are 0–35 units per liter (U/L). When hepatocytes are damaged or killed because of disease, physical exertion, or other factors, AST spills out into the blood. Blood levels of AST that are higher than normal are used to predict the possibility of liver injury. Conditions in which AST levels are increased include alcohol-induced liver injury, cirrhosis, exercise, myopathy, hemolysis, and thyroid disease.^[1][2]