Liver Blood Enzymes
An initial step in detecting liver damage is a simple blood test to determine the presence of certain liver enzymes in the blood. Under normal circumstances, these enzymes reside within the cells of the liver. But when the liver is injured, these enzymes are spilled into the blood stream.
Among the most sensitive and widely used of these liver enzymes are the aminotransferases. They include aspartate aminotransferase (AST or SGOT) and alanine aminotransferase (ALT or SGPT). These enzymes are normally contained within liver cells. If the liver is injured, the liver cells spill the enzymes into blood, raising the enzyme levels in the blood and signaling the liver damage.
What Are The Aminotransferases?
The aminotransferases catalyze chemical reactions in the cells in which an amino group is transferred from a donor molecule to a recipient molecule. Hence, the names “aminotransferases”.
Medical terms can sometimes be confusing, as is the case with these enzymes. Another name for aminotransferase is transaminase. The enzyme aspartate aminotransferase (AST) is also known as serum glutamic oxaloacetic transaminase (SGOT); and alanine aminotransferase (ALT) is also known as serum glutamic pyruvic transaminase (SGPT). To put matters briefly, AST = SGOT and ALT = SGPT.
Normally, Where Are The Aminotransferases?
AST (SGOT) is normally found in a diversity of tissues including liver, heart, muscle, kidney, and brain. It is released into serum when any one of these tissues is damaged. For example, its level in serum rises with heart attacks and with muscle disorders. It is therefore not a highly specific indicator of liver injury.
ALT (SGPT) is, by contrast, normally found largely in the liver. This is not to say that it is exclusively located in liver but that is where it is most concentrated. It is released into the bloodstream as the result of liver injury. It therefore serves as a fairly specific indicator of liver status.
What Are Normal Levels of AST and ALT?
The normal range of values for AST (SGOT) is from 5 to 40 units per liter of serum (the liquid part of the blood).
The normal range of values for ALT (SGPT) is from 7 to 56 units per liter of serum.