Alanine transaminase (ALT) is an enzyme found in the highest amounts in the liver. Injury to the liver results in release of the substance into the blood.

This article discusses the test to measure the amount of ALT in the blood.

Blood is typically drawn from a vein, usually from the inside of the elbow or the back of the hand. The site is cleaned with germ-killing medicine (antiseptic). The health care provider wraps an elastic band around the upper arm to apply pressure to the area and make the vein swell with blood.

Next, the health care provider gently inserts a needle into the vein. The blood collects into an airtight vial or tube attached to the needle. The elastic band is removed from your arm.

Once the blood has been collected, the needle is removed, and the puncture site is covered to stop any bleeding.

In infants or young children, a sharp tool called a lancet may be used to puncture the skin and make it bleed. The blood collects into a small glass tube called a pipette, or onto a slide or test strip. A bandage may be placed over the area if there is any bleeding.

When the needle is inserted to draw blood, some people feel moderate pain, while others feel only a prick or stinging sensation. Afterward, there may be some throbbing.

This test is used to determine if a patient has liver damage.

Normal range can vary according to a number of factors, including age and gender. Normal value ranges may also vary slightly among different laboratories. Talk to your doctor about the meaning of your specific test results.

An increase in ALT levels may be due to:

• Acute pancreatitis
• Celiac disease
• Cirrhosis
• Death of liver tissue (liver necrosis)
• Hepatitis (viral, autoimmune)
• Hereditary hemochromatosis
• Infectious mononucleosis
• Lack of blood flow to the liver (liver ischemia)
• Liver disease
• Liver tumor
• Use of drugs that are poisonous to the liver

There is very little risk involved with having your blood taken. Veins and arteries vary in size from one patient to another and from one side of the body to the other. Taking blood from some people may be more difficult than from others.

Other risks associated with having blood drawn are slight but may include:

• Excessive bleeding
• Fainting or feeling light-headed
• Hematoma (blood accumulating under the skin)
• Infection (a slight risk any time the skin is broken)