In certain disease entities, the liver will be a target organ which will get damaged or will derange its functions in response to the incoming insults. The damaging liver can be the result of either acute insult or more of a chronic insult. Thus, the surest way to identify such damages to the liver is by performing laboratory investigations to assess the changes in biochemical activities related to the liver, more specifically the changes in the liver enzymes.
There are several enzymes which can be detected in the peripheral blood which is either specific or non specific to the liver. ALT, AST, GGT, Alkaline phosphatase and Lactate dehydrogenase are some of the enzymes that can be detected by doing a simple blood analysis.
In liver disease, these enzymes will be detected at a higher level than usual and at certain instances; the ratio between some of the enzymes will also be a useful indicator. The higher values that are seen in disease conditions would be the result of cell damage within the liver which will release the enzymes contained within the damaged cells.
We will now discuss some of the enzymes and how it changes in disease states.
Alanine Transaminase is a liver enzyme present in the hepatocytes or in the liver cells. In acute incidence such as hepatitis and liver damage due to paracetamol poisoning, the ALT levels will rise dramatically and thus indicates relative liver damage.
Also known as Aspartate Transaminase, the enzyme is also present in the liver cells but will also be present in red blood cells, skeletal muscle tissues as well as in cardiac muscles. Thus, isolated elevation of AST do not indicate a liver damage per se but in instances where after elevation the ratio between AST/ALT go beyond 2.0, it indicates towards alcoholic hepatitis whereas if it goes below 1.0, it points towards viral hepatitis.
Gamma glutamyl transpeptidase is an enzyme that will be elevated in most cases of alcoholic insults. The enzyme is specific to the liver cells and it’s a sensitive marker for even minor liver insults.
The enzyme is not specific to the liver but will be present in the bones as well as in the placenta. In the liver, the alkaline phoshatase will be present in the lining cells of the biliary tract and would indicate conditions which lead to cholestasis. Thus, biliary duct obstructions, infiltrative diseases could give rise to high levels of ALP in the circulation.
Although found in many other tissues in the body, Lactate dehydrogenase will also be elevated in liver damage as well. Thus, in combination with other makers, it will be useful in making certain diagnosis.