Liver Blood Enzymes
What Do Elevated AST and ALT Mean?
AST (SGOT) and ALT (SGPT) are sensitive indicators of liver damage from different types of disease. But it must be emphasized that higher-than-normal levels of these liver enzymes should not be automatically equated with liver disease. They may mean liver problems or they may 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 precise levels of these enzymes do not correlate well with the extent of liver damage or the prognosis (outlook). Thus, the exact levels of AST (SGOT) and ALT (SGPT) cannot be used to determine the degree of liver disease or predict the future. For example, 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 residual liver disease. For a contrasting example, patients with chronic hepatitis C infection typically have only a little elevation in their AST and ALT levels. Some of these patients may have quietly developed chronic liver disease such as chronic hepatitis and cirrhosis (advanced scarring of the liver).
What Liver Diseases Cause Abnormal Aminotransferase Levels?
The highest levels of AST and ALT are found with disorders that cause the death of numerous liver cells (extensive hepatic necrosis). This occurs in such conditions as acute viral hepatitis A or B, pronounced liver damage inflicted by toxins as from an overdose of acetaminophen (brand-name Tylenol), and prolonged collapse of the circulatory system (shock) when the liver is deprived of fresh blood bringing oxygen and nutrients. AST and ALT serum levels in these situations can range anywhere from ten times the upper limits of normal to thousands of units/liter.
Mild to moderate elevations of the liver enzymes are commonplace. They are often unexpectedly encountered on routine blood screening tests in otherwise healthy individuals. The AST and 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 to moderate elevations of these liver enzymes is fatty liver. In the United States, the most frequent cause of fatty liver is alcohol abuse. Other causes of fatty liver include diabetes mellitus and obesity. Chronic hepatitis C is also becoming an important cause of mild to moderate liver enzyme elevations.