Serum AST means aspartate aminotransferase, which is highest in the heart muscle and second highest in the liver. AST is increased when there is damage to the liver, for example, in acute viral hepatitis, AST is significantly elevated. In addition, in chronic hepatitis and fatty liver, AST is also increased. In cirrhosis and hepatocellular carcinoma, AST may be mildly elevated. In other diseases, such as infectious mononucleosis, the serum AST may also be elevated. A morning blood test is required to check AST.