Liver enzyme tests

An initial step in detecting liver damage is a very simple blood test to determine the presence of certain liver enzymes in the blood. Under general 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 most widely used of these liver enzymes are the aminotransferases. They include aspartate aminotransferase (AST/ SGOT) and alanine aminotransferase (ALT/ SGPT). These enzymes are normally contained within liver cells themselves. 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.

The aminotransferases catalyze chemical reactions in the cells in which some amino group is transferred from a donor molecule to a recipient molecule. Hence, the names "aminotransferases". 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 explain briefly, AST = SGOT and ALT = SGPT

AST (SGOT) and ALT (SGPT) are sensitive indicators of liver damage from different types of disease. But it must be emphasized that more than normal levels of these liver enzymes should not be automatically equated with liver disease. They may mean liver problems or they may sometimes not. The interpretation of elevated AST and ALT levels depends upon the whole clinical picture and so it is best done by doctors experienced in evaluating liver disease.

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.

The precise levels of these enzymes do not correlate well with the extent of liver damage or the prognosis. Thus, exact levels of AST (SGOT) and ALT (SGPT) cannot be used to determine the degree of liver disease or predict the future. Patients with acute viral hepatitis A may develop very high AST and ALT levels (sometimes in the thousands of units/liter range). But most patients with acute viral hepatitis A recover fully without any residual liver disease. Some of these patients may have quietly developed chronic liver disease such as chronic hepatitis and cirrhosis (advanced scarring of the liver).

Mild to moderate elevations of the liver enzymes are commonplace. They are often encountered on routine blood screening tests in otherwise healthy individuals. The AST / ALT levels in such cases are usually between twice the upper limits of normal and several hundred units/liter. The most common cause of mild/ moderate elevations of these liver enzymes is fatty liver. Other causes of fatty liver include diabetes mellitus & obesity. Chronic hepatitis C is also an important cause of mild to moderate liver enzyme elevations.