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Transaminases, including alanine transaminase (ALT) and aspartate transaminase (AST), are enzymes used to measure liver function. Elevated levels can indicate liver damage, but can also be caused by other conditions or medications. The AST test is more effective in determining alcohol-related liver damage. Different factors can cause variations in levels, and further testing may be necessary to diagnose the cause.
A transaminase is a type of enzyme whose activity is frequently measured, as part of a standard set of tests, to determine liver function. There are several types of transaminases, but the two commonly measured medically are alanine transaminase (ALT) and aspartate transaminase (AST). ALT is primarily located in the liver and is considered a more specific test for liver damage.
ALT and AST are normally held in the liver, but if the organ is damaged, they are released into the bloodstream. As a result, their blood levels are likely to be elevated in cases of liver damage. They can, however, be elevated in other conditions, including cases of thyroid disease, diabetes and heart disease.
Many factors can cause the levels of these enzymes to vary. Men and women have different levels, with men having higher amounts and even being higher for African American men than Caucasian men. Taking certain medications and herbs can cause levels to rise. A slight increase in activity level will usually be followed up by further diagnostic testing, as it may be benign or indicate a serious condition.
The AST test is more effective than the ALT test in determining whether liver damage is due to alcohol abuse. Often, the effects of alcohol abuse are magnified by taking large amounts of the pain reliever acetaminophen. Often the ratio of AST to ALT is used to help diagnose the cause of the liver damage, and if the result is greater than two, it suggests that the liver damage is due to excessive alcohol consumption.
Normally, ALT levels rise more than AST levels during disease processes. Moderate to very high levels of both enzymes can indicate the presence of other conditions affecting the liver, including long-term liver damage, such as cirrhosis, and more recent damage, such as viral hepatitis. They can also indicate liver necrosis or tumor, use of liver-toxic drugs, mononucleosis, or shock. The ALT test can also be used to diagnose lead poisoning.
AST can be elevated by conditions other than liver damage, as it is found in other parts of the body, such as the heart, muscle tissue, and kidneys. Levels of this enzyme can be elevated by something as harmless as exercise. Moderately high levels, however, can indicate a heart attack, lung or kidney damage, certain types of cancer, or Duchenne muscular dystrophy, among many other conditions.
Transaminases are also known as aminotransferases. Amino acids are the building blocks of proteins and contain an amino group, NH2, on them. One of these enzymes transfers that amino group to another compound and is important for protein metabolism in the cell. ALT levels are also known as serum glutamate-pyruvate transaminase (SGPT), while AST levels may be known as serum glutamate-oxaloacetate transaminase (SGOT).
