There are many different 'liver enzymes' that a doctor looks at when evaluating a liver function panel (AKA liver function tests). In fact, the liver function panel is not limited to enzymes, it also measures the levels of total protein, albumin, bilirubin, and other molecules that are all produced by the liver and dispersed through the body by the blood.
When examining the results of the liver function tests, the total protein and albumin levels will not be altered until there is severe damage to the liver. Severe damage means beyond the level of fatty liver disease and progress to liver cirrhosis. At the point of cirrhosis, the liver is so damaged by fibrosis and scar tissue that the ability of the liver to function as an organ is seriously compromised. Thus, the liver will not be able to produce the proteins / albumin, so this will be demonstrated on the laboratory test as a reduced blood level of them. The decrease in the amount of proteins / albumin being produced is the reason why cirrhotic patients get ascites (matching of the abdomen), but that will have to be explained at a different time.
More importantly, what are the 'liver enzymes' that your doctor looks at and what do they mean. Well, normally your liver enzymes should remain in the cells of the liver and should only enter the blood stream in tiny amounts. However, when the liver becomes inflamed and damaged by chronic alcohol exposure, then the cells of the liver (hepatocytes) will break down and spill the enzymes into the blood stream. So, an elevation of 'liver enzymes' is an easy way to determine if your liver has had any damage / inflammation recently.
There are viruses (Hepatitis A, Hepatitis B, and Hepatitis C) that can also cause inflammation in the liver and increase your blood levels of liver enzymes, but there is a simple way to differentiate viral inflammation of the liver versus alcoholic inflammation of the liver that is explained in the following paragraphs.
There are two main enzymes that your doctor will look at in your liver function panel (the other enzymes are not as important unless you have gallstones or other forms of biliary pathology). These enzymes are named Alanine transaminase (ALT) and aspartate transaminase (AST). In the chronic alcoholic patient, these enzymes will be elevated in a certain pattern that is often easy to discern from other causes of liver inflammation (ie viral hepatitis). When the doctor compares the blood level of AST to ALT, the AST will often be elevated by a factor of 2 compared to ALT. For example, in a chronic alcohol user the AST level may be about 120 IU / L, and the doctor would expect the ALT level to be about 60 IU / L.
In viral hepatitis (Hepatitis C), the AST to ALT ratio will be closer to a 1 to 1 ratio and the blood levels are often much higher as compared to in alcohol (usually AST and ALT will be greater than 300 IU / L in patients with viral hepatitis).
I hope this helps some of you who were interested in learning a little bit more about the visit to your doctor. Feel free to ask any questions or ask me to explain something that I did not go over too clear.