What Is an ALT Blood Test
An ALT (alanine transaminase) test measures ALT levels in your blood to screen for liver damage or liver disorders

An ALT (alanine transaminase) test measures ALT levels in your blood to screen for liver damage or liver disorders.

ALT is an enzyme that is mostly produced by the liver and used by the body to convert alanine into pyruvate, which ultimately produces adenosine triphosphate. It plays an important role in metabolism, which is the process that turns food into energy.

ALT is normally present inside the liver cells and released in small amounts according to the body’s needs. However, whenever the liver cells are injured or inflamed, large amounts of ALT may be released into the bloodstream. Therefore, elevated levels of ALT in the blood can be indicative of an underlying liver dysfunction. 

For this reason, physicians often prescribe an ALT blood test to screen for and diagnose a liver disorder even before other clinical features of liver disease appear. ALT tests can help doctors plan further tests and treatment options if necessary.

Why is an ALT blood test done?

The liver is a very important organ that performs crucial functions such as:

  • Synthesis of proteins and cholesterol
  • Synthesis of bile that helps in the digestion of fat
  • Removal of toxins from blood

An ALT test may be performed as a part of liver function tests for routine assessment of liver health. Moreover, it may be ordered to diagnose an underlying liver disease. Common symptoms of liver disease include:

  • Jaundice (yellowish discoloration of the skin, white part of the eyes and mucosa)
  • Nausea and vomiting
  • Pain in the abdomen (especially upper left abdomen)
  • Mass that can be felt in the abdomen
  • Loss of appetite
  • Dark-colored urine
  • Light-colored stools
  • Itchy skin

An ALT test may be performed for people with a high risk of liver damage. Some risk factors for liver damage include:

What do ALT test results indicate?

The normal value of ALT in the blood is 7-55 international units per liter (IU/L), although this range varies according to age and sex. In general, anything higher than 55 IU/L is considered an elevated ALT level. 

Alcoholism or injury to the liver cells may cause a moderate increase in ALT levels. However, diseases such as hepatitis, liver cirrhosis, or tumor/cancer in the liver may cause a much higher increase in ALT levels in the blood.

What are the limitations of the ALT test?

An ALT test is a good first-line screening test to assess liver damage and detect whether there is a problem. However, it is not a reliable indicator of how much damage or fibrosis or scarring of the liver is present. 

In cases such as viral hepatitis A, ALT levels may increase to the value of 2000s and decrease in a month or so. Thus, ALT tests may not provide information as to the severity of certain liver diseases.


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Medically Reviewed on 1/3/2022
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