A liver enzyme is a protein that helps to speed up a chemical reaction in the liver. Liver function tests are blood tests that are used to evaluate various functions of the liver - for example, metabolism, storage, filtration and excretion, which are often performed by liver enzymes. However, not all liver function tests are measures of enzyme function.
The liver is an important internal organ because it performs many functions. It helps detoxify the many toxins in the body, makes proteins that are used to help clot the blood (clotting factors) and other proteins that help draw fluid into our blood vessels (e.g., albumin).
Liver function tests are blood tests that include alkaline phosphatase, prothrombin time (PT, a measure of blood clotting), serum bilirubin and serum albumin. The most commonly used indicators of liver damage are the alanine aminotransferase (ALT) and aspartate aminotransferase (AST), formally referred to as SPGT and SGOT. These are enzymes normally found in liver cells that leak out of these cells and make their way to the blood when liver cells are injured. The ALT is felt to be a more specific indicator of liver inflammation, as AST is also found in other organs, such as the heart and skeletal muscle.
In acute injury to the liver, as in viral hepatitis, the level of the ALT and AST may be used as a general measure of the degree of liver inflammation or damage. In chronic liver disease, this is not the case, for these enzymes may be entirely within the normal range, even in the presence of cirrhosis (scarring of the liver).
Increased levels of ALT and AST can have a large number of clinical implications. Elevated levels might involve hepatocellular disease, active cirrhosis, metastatic liver tumor, infection or toxic hepatitis, severe burns, pancreatitis, myocardial infarction (heart attack), trauma, severe burns, acute hemolytic anemia, crushing injuries, gangrene or shock.
Alkaline phosphatase is the most frequently used test to detect obstruction in the biliary system. Elevation of this enzyme may be found in a large number of disorders as common as gallstone disease, alcohol abuse and drug-induced hepatitis, or in less common disorders, such as primary biliary cirrhosis or biliary tumors. Although this enzyme is found both in the liver and the bile, it leaks into the bloodstream in a manner similar to that of the ALT and AST. Alkaline phosphatase is also found in other organs, such as bone, placenta and intestine.
Prothrombin time (PT) is a one measure of blood clotting. It may be elevated when there is damage to the liver, meaning that there is a greater tendency to bleed. PT is also used to monitor the appropriate dose of coumadin (warfarin) for certain patients who need blood-thinners (anti-coagulation).
Low serum albumin may cause blood vessels to be leaky and allow fluid to accumulate in the abdomen (ascites) or elsewhere in the body.
Serum bilirubin is usually elevated in patients with jaundice.
What are the normal ranges of these enzymes?
Are the enzymes slightly elevated or severely elevated?
What is the cause of the elevated liver enzymes?
Does the enzyme elevation mean inflammation to the liver or damage to the liver?
If the elevated enzymes indicate damage to the liver, how much damage has occurred?