The alanine transaminase (ALT) blood test measures the level of the enzyme ALT in the blood.
How the Test is Performed
A blood sample is needed.
How the Test will Feel
When the needle is inserted to draw blood, some people feel moderate pain. Others feel only a prick or stinging. Afterward, there may be some throbbing or a slight bruise. This soon goes away.
How to Prepare for the Test
No special preparation is needed.
The normal range is:
- Male: 10 to 40 U/L (0.17 to 0.67 µkat/L)
- Female: 4 to 19 U/L (0.07 to 0.32 µkat/L)
Normal value ranges may vary slightly among different laboratories. Some labs use different measurements or may test different samples. Talk to your health care provider about the meaning of your specific test results.
There is very little risk involved with having your blood taken. Veins and arteries vary in size from one person 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:
- Bleeding from where the needle was inserted
- Fainting or feeling lightheaded
- Hematoma (blood collecting under the skin)
- Infection (rare)
What Abnormal Results Mean
An increased ALT level is often a sign of liver disease. Liver disease is even more likely when the levels of substances checked by other liver blood tests have also increased.
An increased ALT level may be due to any of the following:
- Scarring of the liver (cirrhosis)
- Death of liver tissue
- Swollen and inflamed liver (hepatitis)
- Too much iron in the body (hemochromatosis)
- Too much fat in the liver (fatty liver)
- Lack of blood flow to the liver (liver ischemia)
- Liver tumor or cancer
- Use of drugs that are toxic to the liver
- Mononucleosis ("mono")
- Swollen and inflamed pancreas (pancreatitis)
Why the Test is Performed
ALT is an enzyme found in a high level in the liver. Injury to the liver results in release of ALT into the blood.
This test is used to determine if a person has liver damage.
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Pincus MR, Tierno PM, Gleeson E, Bowne WB, Bluth MH. Evaluation of liver function. In: McPherson RA, Pincus MR, eds. Henry's Clinical Diagnosis and Management by Laboratory Methods. 23rd ed. St Louis, MO: Elsevier; 2017:chap 21.
Pratt DS. Liver chemistry and function tests. In: Feldman M, Friedman LS, Brandt LJ, eds. Sleisenger and Fordtran's Gastrointestinal and Liver Disease. 10th ed. Philadelphia, PA: Elsevier Saunders; 2016:chap 73.