A protein is a large molecule synthesized by smaller molecules called amino acids. The DNA in cells codes for the synthesis of proteins by telling the cells what order to put the amino acids in. Proteins have numerous functions. One is as an enzyme. An enzyme speeds up chemical reactions, such as breaking down sugar for energy, or building or breaking down fat. The liver cells contain many enzymes that function to maintain health. Elevated levels can be indicative of disease and require consultation with a physician.
Functions of Liver Enzymes
Liver enzymes have a number of functions; some are shared by most cell types, while others are more unique to the liver. Many of the enzymes unique to the liver help detoxify the blood. The intestines absorb food into a series of blood vessels called the portal system, which lead directly to the liver. The direct path from the intestines to the liver helps the body to change the chemical structure of ingested chemicals. Enzymes in the liver add or take away oxygen or hydrogen, break bonds in chemicals, add chemical groups and so forth, in an attempt to modify any ingested toxins. Other enzymes help the body utilize or store nutrients and energy containing compounds.
Measurement
There are several tissue types in the liver. The vascular tissues provide the blood supply. The hepatocytes are the cells of the liver. The biliary tissues transport bile, a digestive fluid, to the gallbladder and intestine. When damage occurs to the liver, or a specific tissue type, the cells can burst open, or lyse, releasing their contents, including their enzymes, into the bloodstream. A blood test can measure the levels of liver enzymes. Commonly measured enzymes include AST, ALT and alkaline phosphatase. Others can be measured as needed.
Diagnosis
The diagnosis of diseases, including liver disease, depends on a medical history, physical exam, and laboratory and imaging studies. Elevated liver enzymes suggest a particular diagnosis, depending on how high the enzymes become, the time course, and pattern of elevation. For example, very high levels of ALT and AST, usually with ALT higher, suggest viral hepatitis or a liver toxin such as acetaminophen. Low to moderately high AST and ALT with AST higher suggest alcoholism. An elevated alkaline phosphatase is seen in damage to the biliary system.
Treatment
Elevated liver enzymes are not likely dangerous, but the underlying liver damage and contributing condition need treatment. For example, infections may require antibiotics or surgical drainage. Autoimmune conditions in which the body attacks liver tissues may require immune modulating drugs. Complete liver failure requires a liver transplant with immune suppressing drugs to prevent rejection.
References
- "Harrison's Principles of Internal Medicine"; Anthony S Fauci, et al.; 17th Ed 2008
- "Henry's Clinical Diagnosis and Management by Laboratory Methods"; Richard A. McPherson, et al.; 21st Ed 2006
