Once a sample of blood is drawn from a vein, the physician can order several laboratory tests, including the liver enzymes function test. An increase in liver enzymes in the bloodstream can indicate injured liver cells. The amount of increase depends upon the extent and type of injury.
The Liver Enzymes
The medical term "liver enzymes" refers to the enzymes known as alanine aminotransferase and aspartate aminotransferase. They are called enzymes because they are proteins that the cells use to make a reaction go faster. Alanine aminotransferase, or ALT, is primarily found inside the liver. Aspartate aminotransferase, or AST, on the other hand, is located inside the liver and also in the kidneys, skeletal muscle and heart.
What an Increase in Liver Enzymes Means
There is usually a low amount of liver enzymes in the bloodstream, but whenever there is damage to the membrane of the liver cells, the liver enzymes within the cells are able to escape and are released into the blood. Thus, any injury to the cells of the liver can lead to an increase in liver enzymes.
Liver Enzyme Values
The normal range for the liver enzymes is 7 to 40 U/L. Liver disorders can cause the level to increase as much as 300 U/L, while a level as high as 1,000 U/L can be the result of liver damage due to drugs, toxins, low blood flow or viral hepatitis. If the AST enzyme is three times more than ALT, the person most likely has alcoholic liver disease. In addition, an increased ALT means liver damage, while an increase in AST could mean damage in the liver, kidneys, skeletal muscle or heart.
The Most Common Cause of Increased Liver Enzymes
Most of the time, an increase in ALT and AST is temporary and mild. Thus, it does not represent any serious liver disorder. An increase in liver enzymes most often results from nonprescription pain medications, alcohol, hepatitis, obesity, statin cholesterol-lowering medication, heart failure and nonalcoholic fatty liver disease. Hepatitis is the inflammation of the liver; while the liver accumulates fat in nonalcoholic fatty liver disease, but it is not due to alcohol.
References
- "Clinical Anesthesiology"; Wayne Kleinman, M.D., Gary Nitti, M.D. et al; 2006
- "Harrison's Principles of Internal Medicine"; Anthony Fauci, M.D., Dennis Kasper, M.D., Dan Longo, M.D. et al.; 2008
- MayoClinic.com; Elevated liver enzymes; May 5, 2011
