Liver Function

ALT and AST - Liver Function Information

Table of Contents

What is ALT?
What is AST?
What is the purpose of the blood serum test?
Causes of Elevated ALT or AST Values in Asymptomatic Patients
ALT Levels
Typical AST or ALT Values in Disease

Additional Information

What is ALT?

ALT (Alanine Aminotransferase) is an enzyme that appears in liver cells, with lesser amounts in the kidneys, heart, and skeletal muscles, and is a relatively specific indicator of acute liver cell damage. When such damage occurs, ALT is released from the liver cells into the bloodstream, often before jaundice appears.

What is AST?

AST (Aspartate Aminotransferase) is found in many body tissues including the heart, muscle, kidney, brain, and lung. It is also present in the liver. When body tissue or an organ such as the heart or liver is damaged, additional AST is released into the bloodstream. The amount of AST in the blood is directly related to the extent of the tissue damage.

What is the purpose of the blood serum test?

ALT and AST are elevated even before the clinical signs and symptoms of disease, such as cardiovascular disease, liver disease and muscle disease. The purpose of the blood serum test is to help detect and evaluate treatment of acute hepatic disease, especially hepatitis, and cirrhosis without jaundice. An inflamed liver is called hepatitis. Trauma can cause this, along with drugs (even aspirin), viruses, bacteria, bile, and toxins. Many medications produce hepatic injury by competitively interfering with cellular metabolism.

To help distinguish between myocardial (heart) and jaundice (liver tissue).

Also to assess hepatotoxicity of some drugs.

Causes of Elevated ALT or AST Values in Asymptomatic Patients

Autoimmune hepatitis, Hepatitis B, Hepatitis C, Drugs or Toxins, Ethanol (Alcohol), Fatty liver, Growths (i.e., Tumors), Hemodynamic Disorder (congestive heart failure), Iron (hemochromatosis), Copper (Wilson's disease) or Alpha-Antitrypsin Deficiency, Muscle injury.

ALT Levels

Alt levels by a commonly used method range from 10 to 32 U/L; in women, from 9 to 24 U/L. (There does exist differing ranges used by various laboratories.) The normal range for infants is twice that of adults.

Very High ALT Levels (up to 50 times normal) suggest viral or severe drug-induced hepatitis, or hepatic disease with extensive necrosis (death of liver cells).
Moderate-to-high levels may indicate infectious mononucleosis, chronic hepatitis, intrahepatic cholestasis, cholecystitis, early or improving acute viral hepatitis, or severe hepatic congestion due to heart failure.
Slight-to-moderate elevations (usually with higher increases in AST levels) may appear in any condition that produces acute hepatocellular (liver cell) injury, such as active cirrhosis, and drug-induced or alcoholic hepatitis.
Marginal elevations occasionally occur in acute myocardial infarction (heart attack), reflecting secondary hepatic congestion or the release or small amounts of ALT from the heart tissue.

Typical AST or ALT Values in Disease

Typical serum aspartate aminotransferase (AST) or alanine aminotransferase (ALT) values for various diseases. Note that the horizontal axis is a log scale. As shown, the aminotransferases are often normal in patients with cirrhosis. In patients with uncomplicated alcoholic hepatitis, the AST value is rarely greater than 500 U per L and is usually no more than 200 to 300 U per L. The highest peak aminotransferase values are found in patients with acute ischemic or toxic liver injury.

The higher the AST-to-ALT ratio, the greater the likelihood that alcohol is contributing to the abnormal LFTs. In the absence of alcohol intake, an increased AST-to-ALT ratio is often found in patients with cirrhosis. That is also why it is important to have both tests performed. The elevated AST-to-ALT ratio in alcoholic liver disease results in part from the depletion of vitamin B6 (pyridoxine) in chronic alcoholics. PT (Prothrombin Time) does not become abnormal until more than 80% of liver synthetic capacity is lost. Which makes the PT a relatively insensitive marker of liver dysfunction. PT is very useful for following liver function in patients with acute liver failure, because prolongation may be a sign of serious liver dysfunction. An elevated PT can result from a vitamin K deficiency. When there are problems with ALT and AST the LFTS are good tests to be taken.

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