The normal levels for the most common liver enzymes, aspartate aminotransferase and alanine aminotransferase, are 10 to 40 units per liter and 7 to 56 units per liter, says eMedicineHealth. Mild elevations two to three times the size of those figures do occur, and severe levels typically reach over 1000.
The normal ranges of the AST and ALT enzymes may vary between laboratories around the world, according to MedicineNet.com.
Enzymes are proteins that exist in various areas of the body to provide essential acceleration to many chemical reactions that occur in the body, according to MedicineNet.com. The aminotransferase enzymes are kept in cells that reside in the liver. This is where the enzymes reside when their levels are within the normal range. When the liver experiences trauma, the enzymes enter the bloodstream, and their levels spike. The severity of the spike revealed in blood tests may indicate whether or not the patient is suffering from the early stages of liver disease, but this is mainly determined by the patient's ALT levels.
The ALT enzymes are mainly found in the liver, claims MedicineNet.com. This is why determining ALT levels is more essential than determining AST levels when diagnosing liver conditions, as the AST enzymes can also be found in the heart, kidneys, brain and various muscles of the body.
Experts from the American Association for Clinical Chemistry say that alkaline phosphatase is found in the edges of the cells that link together to form the bile ducts as well as in bone tissue. A bone or liver disorder sometimes causes an elevated level of this enzyme. MedlinePlus says its normal range in the blood is 44 to 147 international units per liter.
Aspartate aminotransferase is found in the liver, kidneys, skeletal muscles and heart. People who have had heart attacks, viral hepatitis or acute liver damage often have high levels of this enzyme, according to the Mayo Clinic. The normal range for this enzyme is 10 to 34 international units per liter, according to the MedlinePlus website.