Aspartate aminotransferase (AST) is an enzyme found mainly in the liver and heart. The liver uses AST and other enzymes to make proteins and metabolize amino acids. Increased AST indicates liver damage or disease, as well as damage to the heart muscle. Cellular damage to either organ causes the AST to be released into the bloodstream.
Reference Values
Normal AST values for men and women differ slightly. For men, the normal range is 8-46 U/L. The normal range for women is 7-34 U/L. The definition of normal lab values may vary slightly from one lab to another.
Indications For AST Testing
AST may be ordered to monitor possible adverse effects of certain medications known to affect the liver in high doses, such as acetaminaphen. Other indications for testing include symptoms of possible liver conditions, such as jaundice, dark urine, light-colored bowel movements and vomiting blood. Exposure to hepatitis or excessive alcohol intake would also be indication for testing AST.
Liver Conditions Affecting AST
AST levels are elevated in mononucleosis, liver tumors, cirrhosis, hepatitis and traumatic injury to the liver. Shock, in which circulatory collapse delivers less blood and oxygen to the liver, also affects AST. One of the main causes of elevated AST values is fatty liver. Fatty liver results from prolonged alcohol abuse, obesity and diabetes.
Warning
According to Dr. Siamak Nabili, medical author on medicinenet.com, higher levels do not necessarily indicate the extent of liver damage. For example, a patient with acute hepatitis A may have very high AST levels, up into the thousands. Most patients with hepatitis A fully recover with no permanent damage to the liver.
In contrast, a patient with chronic hepatitis C usually has only a slight elevation in AST. These patients may develop chronic hepatitis and cirrhosis.
Considerations
Elevated AST alone is not an absolute indicator of liver damage. Before a diagnosis is made, a complete history and physical should be obtained, along with other blood work. Additional studies such as x-ray or CT (cat scan) may be ordered to confirm diagnosis.
Other Drugs Affecting AST
Many medications affect liver function and should be used with caution in patients with known liver dysfunction. A few of the more popular medications affecting the liver include aspirin, ibuprofen, naproxen, statin drugs to lower cholesterol, certain cardiac drugs and tricyclic antidepressants.
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