ALT (Alanine Aminotransferase) Test

Written by Karla Blocka | Published on August 15, 2012
Medically Reviewed by George Krucik, MD

What Is an Alanine Aminotransferase (ALT) Test?

An alanine aminotransferase (ALT) test measures the level of ALT enzyme in your blood. ALT is an enzyme produced by liver cells. It helps the body metabolize proteins. If the liver is damaged or not functioning properly, ALT is released into the blood. This causes ALT levels to increase.

The alanine aminotransferase (ALT) test is used to evaluate liver function. The test is also known as a serum glutamate pyruvate transaminase (SGPT) test or alanine transaminase test.

Why the ALT Test Is Performed

The ALT test is used to evaluate whether a patient has liver damage.

Liver damage causes an elevation in ALT levels. However, the test does not show how much damage there is or how much fibrosis (scarring) is present. The test also does not predict how severe the liver damage will become.

An ALT test may be performed regularly to:

  • monitor the activity of liver diseases, such as hepatitis
  • assess whether treatment for liver disease should be started
  • evaluate how well treatment is working

An increased level of ALT in the blood is a sign of liver damage. However, not all individuals with liver disease will have increased ALT. Many patients with severe liver disease or cirrhosis have normal ALT levels.

How the ALT Test Is Performed

Certain medications and foods may affect ALT levels in the blood. Therefore, your doctor may direct you to avoid certain medications or fast for a period of time prior to the ALT test.

The ALT test is performed on a blood sample. An elastic band is wrapped around your upper arm to stop the flow of blood and make the veins in your arm more visible. This makes it easier to insert the needle.

Alcohol is used to clean your skin where the needle will be inserted. The needle is inserted into the vein. This may cause a brief pinching or stinging sensation. You may not feel anything at all.

A tube is attached to the end of the needle to collect the blood. Sometimes more than one tube may be required. After enough blood has been collected, the needle and the elastic band is removed and cotton or gauze is placed on the site of the puncture. Pressure is applied and a bandage or tape is used to keep the cotton or gauze in place.

The blood sample is sent to a laboratory for analysis. Test results are then sent from the laboratory to your doctor. Your doctor may request an appointment with you to discuss the results.

Risks Associated with the ALT Test

There is little risk involved with having a blood test. Sometimes bruising occurs where the needle was inserted into the vein. The risk of bruising can be minimized by applying pressure to the injection site for several minutes after the needle is removed.

In very rare cases, the following complications may occur:

  • excessive bleeding
  • hematoma (the accumulation of blood beneath the skin)
  • lightheadedness or fainting
  • infection

ALT Test Results

Normal Results

A normal ALT test result is a measurement of 7 to 55 units per liter (U/L). The normal range can be affected by different factors, such as gender and age. It is important to discuss your specific results with your doctor.

Abnormal Results

Higher-than-normal amounts of ALT can be a sign of liver damage. Increased levels of ALT may be a result of:

  • hepatitis
  • cirrhosis
  • liver tissue death (necrosis)
  • tumor or cancer in the liver
  • toxic medications
  • hemochromatosis
  • mononucleosis
  • pancreatitis (inflamed and swollen pancreas)
  • lack of blood flow to the liver (liver ischemia)
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