The ALT and AST are enzymes that are located in liver cells and leak out and make their way into the general circulation when liver cells are injured. The ALT is thought to be a more specific indicator of liver inflammation, since the AST may be elevated in diseases of other organs such as the heart or muscle. In acute liver injury, such as acute viral hepatitis, the ALT and AST may be elevated to the high 100s or over 1,000 U/L. In chronic hepatitis or cirrhosis, the elevation of these enzymes may be minimal (less than 2-3 times normal) or moderate (100-300 U/L). Mild or moderate elevations of ALT or AST are nonspecific and may be caused by a wide range of liver diseases. ALT and AST are often used to monitor the course of chronic hepatitis and the response to treatments, such as prednisone and interferon.

Alanine Transaminase (ALT or SGPT) Alanine transaminase is an enzyme that is important in the processing of proteins. This enzyme is found in large amounts in the liver, and small amounts of this enzyme are also found in the heart, muscle, and kidney. When the liver is injured or inflamed, the levels of ALT in blood usually rise; therefore, this test is done to check for signs of liver disease.

Aspartate Transaminase (AST or SGOT) Aspartate transaminase is an enzyme that plays a role in many aspects of body metabolism. This enzyme is found in many body tissues including the heart, muscle, kidney, brain, and lung. It is also present in the liver. If there is cell injury or death in any of these tissues, AST is released into the bloodstream; therefore, elevated AST levels can be seen in a variety of conditions, including liver disease. For example, the AST may be elevated in viral hepatitis, mononucleosis, or following a heart attack.