A transaminase is a type of enzyme whose activity is frequently measured, as part of a standard series of tests, to determine liver function. There are a number of different types of transaminases, but the two commonly measured medically are alanine transaminase (ALT) and aspartate transaminase (AST). ALT is primarily localized to the liver and is considered a more specific test for liver damage.
ALT and AST are normally contained within the liver, but if the organ is damaged, they are released into the bloodstream. As a result, their levels in the blood are likely to be elevated if there is liver injury. They may, however, be elevated under other conditions, including in 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 they are even higher for African-American men than Caucasian men. Taking certain medications and herbs may cause an increase in levels. A slight increase in level activity will usually be followed by further diagnostic tests, since it could be benign or indicate a severe condition.
The AST test is more effective than the ALT one at determining whether liver damage is due to alcohol abuse. Often, the effects of alcohol abuse are magnified by taking large quantities of the pain reliever acetaminophen. Frequently the ratio of AST to ALT is used to help in diagnosing the cause of 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 higher than those of AST during disease processes. Moderate to very high levels of both enzymes can indicate the presence of other conditions affecting the liver, including both liver damage over the long term — such as cirrhosis — and more recent damage, such as viral hepatitis. They can also indicate liver necrosis or tumor, the use of drugs that are toxic to the liver, mononucleosis, or shock. The ALT test can also be used to diagnose lead poisoning.
AST can be elevated from conditions other than liver damage, since it is found in other parts of the body, such as the heart, muscle tissue, and kidneys. Levels of this enzyme can be elevated from something as harmless as exercise. Moderately high levels, however, can indicate a heart attack, lung or kidney damage, some types of cancer, or Duchenne’s muscular dystrophy, among many other conditions.
The 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 those of AST can be known as serum glutamate-oxaloacetate transaminase (SGOT).