Liver Blood Tests

What are the basic functions of the liver?

The liver is located in the right upper portion of the abdominal cavity just beneath the rib cage. The liver has many functions vital to life. Some of the important functions of the human liver are:

Detoxification of blood
Production of important clotting factors, albumin, and many other important proteins
Metabolizing (processing) medications and nutrients
Processing of waste products of hemoglobin and other cells
Storing of vitamins, fat, cholesterol, and bile
Production of glucose (gluconeogenesis or glucose synthesis/release during starvation)

What are common liver blood tests?

Liver blood tests are some of the most commonly performed blood tests. These tests can be used to assess liver functions or liver injury. An initial step in detecting liver damage is a simple blood test to determine the level of certain liver enzymes (proteins) in the blood. Under normal circumstances, these enzymes mostly reside within the cells of the liver. But when the liver is injured for any reason, these enzymes are spilled into the bloodstream. Enzymes are proteins that are present throughout the body, each with a unique function. Enzymes help to speed up (catalyze) routine and vital chemical reactions in the body.

Among the most sensitive and widely used liver enzymes are aminotransferases. They include aspartate aminotransferase (AST or SGOT) and alanine aminotransferase (ALT or SGPT). These enzymes are normally predominantly contained within liver cells and to a lesser degree in muscle cells. If the liver is injured or damaged, the liver cells spill these enzymes into the blood, raising the AST and ALT enzyme blood levels and signaling liver disease.

Other blood tests about the liver are measurements of some of the other enzymes found in the liver. In addition to AST and ALT, alkaline phosphatase, 5′ nucleotidase, and gamma-glutamyl transpeptidase (GGT) are a few of the other enzymes located in the liver. The focus of this article is mainly on the most common liver enzymes, AST and ALT.

What are the basic functions of the liver?

The liver is located in the right upper portion of the abdominal cavity just beneath the rib cage. The liver has many functions vital to life. Some of the important functions of the human liver are:

Detoxification of blood
Production of important clotting factors, albumin, and many other important proteins
Metabolizing (processing) medications and nutrients
Processing of waste products of hemoglobin and other cells
Storing of vitamins, fat, cholesterol, and bile
Production of glucose (gluconeogenesis or glucose synthesis/release during starvation)

What are common liver blood tests?

When should I be concerned about high AST and ALT?

AST (SGOT) and ALT (SGPT) are reasonably sensitive indicators of liver damage or injury from different types of diseases or conditions, and collectively they are termed liver tests or liver blood tests. However, higher-than-normal levels of these liver enzymes are not automatically equated with liver disease. They may mean liver problems or they may not. For example, elevations of these enzymes can occur with muscle damage. The interpretation of elevated AST and ALT results depends upon the entire clinical evaluation of an individual, and so it is best done by physicians experienced in evaluating liver disease and muscle disease.

Moreover, the precise levels of these liver enzyme tests do not correlate well with the extent of liver problems or the prognosis (outlook) so, the exact levels of AST (SGOT) and ALT (SGPT) cannot be used to determine the degree of liver disease or predict the future prognosis for liver function. For example, individuals with acute viral hepatitis A may develop very high AST and ALT levels (sometimes in the thousands of units/liter range), but most people with acute viral hepatitis A recover fully without residual liver disease. Conversely, people with chronic hepatitis C infection typically have only a little elevation in their AST and ALT levels while having a substantial liver injury and even advanced scarring of the liver (cirrhosis) from ongoing minor inflammation of the liver.

Do AST and ALT test results indicate liver function?

It is important to clarify that ALT and AST levels do not completely reflect the function of the liver, even though in the medical community and medical publications they commonly are referred to as liver function tests. Even in conditions when AST and ALT are very elevated, the liver still may function properly.

Consequently, if you have “elevated liver enzymes” or a high or abnormal liver test, you need to ask your physician exactly what all the tests indicate.