Aspartate Transferase

Overview

Aspartate Transferase (AST) is an enzyme normally found in red blood cells, liver, heart, muscle tissue, pancreas, and kidneys. These enzymes catalyze chemical reactions in the body in which an amino group is transferred from a donor molecule to a recipient molecule.

The blood test for aspartate aminotransferase (AST) is usually used to detect liver damage. It is often ordered in conjunction with another liver enzyme, alanine aminotransferase (ALT), or as part of a liver panel to screen for and/or help diagnose liver disorders.

AST and ALT are considered to be two of the most important tests to detect liver injury, and they may be used to distinguish between different causes of liver damage and to distinguish liver injury from damage to heart or muscle.

Why it is done

An aspartate aminotransferase (AST) test is done to:

  • Check for liver damage.
  • Help identify liver disease, especially hepatitis and cirrhosis. Liver disease may produce symptoms such as pain in the upper abdomen,nausea, vomiting, and sometimes jaundice.
  • Check on the success of treatment for liver disease.
  • Find out whether jaundice was caused by a blood disorder or liver disease.
  • Keep track of the effects of medicines that can damage the liver.

AST levels are often compared with results of other tests, such as alkaline phosphatase (ALP), total protein, and bilirubin to help determine which form of liver disease is present.

What does the test result mean?

Normally, levels of AST in the blood are low.

Very high levels of AST (more than 10 times normal) are usually due to acute hepatitis, sometimes due to a viral infection. With acute hepatitis, AST levels usually stay high for about 1-2 months but can take as long as 3-6 months to return to normal. Levels of AST may also be markedly elevated (often over 100 times normal) as a result of exposure to drugs or other substances that are toxic to the liver as well as in conditions that cause decreased blood flow (ischemia) to the liver.

With chronic hepatitis, AST levels are usually not as high, often less than 4 times normal, and are more likely to be normal than are ALT levels. AST often varies between normal and slightly increased with chronic hepatitis, so the test may be ordered frequently to determine the pattern. Such moderate increases may also be seen in other diseases of the liver, especially when the bile ducts are blocked, or with cirrhosis or certain cancers of the liver. AST may also increase after heart attacks and with muscle injury, usually to a much greater degree than ALT.