Alanine Aminotransferase

Alanine aminotransferase (ALT) is an enzyme found primarily in the liver and kidney. It was originally referred to as serum glutamic pyruvic transaminase (SGPT). Normally, a low level of ALT exists in the serum. ALT is increased with liver damage and is used to screen for and/or monitor liver disease. Alanine aminotransferase (ALT) is usually measured concurrently with AST as part of a liver function panel to determine the source of organ damage. ^[1]

Normal findings

Adult/child: 4-36 units/L at 37°C, or 4-36 units/L (SI units) ^[2]

Elderly: May be slightly higher than an adult ^[2]

Infant: May be twofold the level of an adult ^[2]

Conditions associated with very high levels of ALT are as follows:

• Liver damage (acute viral hepatitis, toxins/drugs including acetaminophen overdose, acute fulminant hepatitis) ^{[3, 4]}

• Peak levels do not necessarily correlate with prognosis.

• Tumor necrosis

Conditions associated with moderately high levels of ALT are as follows:

• Chronic liver disease

• Alcohol abuse

• Cholestasis

• Heart damage (heart attack, heart failure)

• Kidney damage

• Muscle injury

• Hemolysis

• Heatstroke (level dependent on extent of tissue damage)

• High consumption of vitamin A

Conditions associated with slightly high levels of ALT are as follows:

• Fatty change in the liver

• Alcohol abuse

• Cirrhosis

• Mononucleosis

• Drugs (ie, statins, aspirin, barbiturates, HIV medication, herbs)

Specimen: Serum/plasma

Collection: Red top

Panels: Liver panel, hepatic function panel, AST/ALT ratio

Description

ALT is an enzyme found primarily in the liver and kidney. It was originally referred to as serum glutamic pyruvic transaminase (SGPT). Normally, a low level of ALT is found in the serum. ALT is increased with liver damage and is used to screen for and/or monitor liver disease.

Alanine aminotransferase (ALT) is usually measured concurrently with AST as part of a liver function panel to determine the source of organ damage. ALT is more specific for liver damage since it is found primarily in the liver and has a longer half-life, whereas AST is found in many other organs. Liver diseases in which AST is higher than ALT include alcohol-induced liver damage, cirrhosis, and liver tumors. ALT catalyzes the transfer of an amino group from alanine to a-ketoglutarate, the products of this reversible transamination reaction being pyruvate and glutamate, as seen in the formula below:

• glutamate + pyruvate ⇌ α-ketoglutarate + alanine

Of note, synthesis of ALT is dependent on vitamin B6 (pyridoxal phosphate) and will be decreased in the setting of low vitamin B6 and cirrhosis.

Indications/Applications

When liver disease is suspected (ie, jaundice, fatigue, nausea, vomiting, dark urine, pale colored stools, itching, ascites, mental changes, history of alcohol abuse, suspected acetaminophen overdose, family history of liver disease, exposure to hepatitis viruses)

To monitor liver function (ie, use of potentially hepatotoxic drugs, treatment of or status of chronic liver disease, hepatitis, alcohol-induced liver disease, cirrhosis, fatty liver disease, hepatic failure, Wilson’s disease, hemochromatosis)

Considerations

The AST:ALT ratio (De Ritis ratio) can be used to determine alcohol-induced liver disease, with AST:ALT ratio greater than 2.

Elevated AST and normal ALT can indicate a normal liver but damage to other organs and/or hemolysis.

Both AST and ALT are dependent on vitamin B6 (pyridoxal phosphate). Assays for AST and ALT assume adequate levels of vitamin B6 to accurately measure AST and ALT levels. Vitamin B6 depletion can result in artificially low AST and ALT levels.

Hemolyzed specimens should not be used.

ALT should be run the day of collection since activity is lost at room temperature, 4 º C, and -25 º C.