ALT (alanine aminotransferase) is a liver enzyme that occurs inside hepatocytes or liver cells. Normal blood levels of ALT are 7–56 units per liter (U/L). When hepatocytes are damaged or killed because of disease, physical exertion, or other factors, ALT spills out into the blood. Blood levels of ALT that are higher than normal are used to predict the possibility of liver injury. ALT levels are increased in diseases such as alcohol-induced liver injury, nonalcoholic fatty liver disease (NAFLD), nonalcoholic steatohepatitis (NASH), hepatitis, drug-induced liver injury, celiac disease, Wilson disease, and hemochromatosis.^[1][2]