Aspartate Aminortransferase, also called AST, is a commonly performed blood test that assesses the function of the liver. In this article, we shall take a brief look at this test and its clinical implications.
What is AST?
AST is an enzyme that is secreted in high quantities by the liver. Consequently, in the event that the liver is not working to its full capacity, or is damaged due to some reason or another, the levels of AST in the blood will rise.
AST is also present in the heart and the muscles. Damage to these structures can also elevate the levels of AST.
How is the AST Level Estimated?
AST is checked with the help of a simple blood test. Blood is withdrawn using a syringe and needle from a vein in the arm under sterile conditions. The sample that is drawn is put into sterile bottle and sent to the biochemistry laboratory for analysis. The injection will be slightly painful, but the symptoms will subside immediately after the needle is removed.
Before the tests, patients may need to stop medications that affect the liver. If patients have to take the medications, then this needs to be taken into consideration when interpreting the results. Herbal medicines can also affect the values.
An AST test forms a part of the liver function tests panel, and is often combined with alanine transaminase and bilirubin. In other words, if the function of the liver needs to be assessed, AST is one of the tests that is performed.
Clinical Implications
The normal range of AST lies between 10-34 international units per litre (10-34 IU/L). These ranges may vary between laboratories. This level is fairly low, which is why elevated levels are significant.
Elevated levels of AST are seen in conditions such as liver necrosis, cirrhosis and hemochromatosis. Inflammation of the liver i.e. hepatitis is also another recognised cause. Liver cancer can also increase AST levels. A reduction in the flow of blood to the liver, i.e. liver ischemia can cause a rise in levels of AST.
Inflammation of the pancreas, called pancreatitis can increase AST levels. Heart attacks are also a well recognised cause, though AST levels are not routinely measured in these cases as they do not aid a diagnosis as such.
Non specific rises in AST levels can be seen following surgery and in patients who have suffered from burns. Epilepsy is also a cause.
The AST is a better test than ALT when detecting damage to the liver. In conclusion, AST is a useful test in detecting damage to the liver.