All content on Lab Tests Online has been reviewed and approved by our Editorial Review Board.
The Test Sample
What is being tested?
Alanine aminotransferase (ALT) is an enzyme found mostly in the cells of the liver and kidney. Much smaller amounts of it are also found in the heart and muscles. In healthy individuals, ALT levels in the blood are low. When the liver is damaged, ALT is released into the bloodstream, usually before more obvious signs of liver damage occur, such as jaundice. This makes ALT a useful test for detecting liver damage.
The liver is a vital organ located in the upper right-hand side of the abdominal area. It is involved in many important functions in the body. The liver helps to process the body's nutrients, manufactures bile to help digest fats, produces many important proteins such as blood clotting factors, and breaks down potentially toxic substances into harmless ones that the body can use or excrete.
A number of conditions can cause damage to liver cells, resulting in an increase in ALT. The test is most useful in detecting damage due to hepatitis or as a result of drugs or other substances that are toxic to the liver.
ALT is commonly tested in conjunction with aspartate aminotransferase (AST), another liver enzyme, as part of a liver panel. Both ALT and AST levels usually rise whenever the liver is being damaged, although ALT is more specific for the liver and, in some cases, may be the only one of the two to be increased. An AST/ALT ratio may be calculated to aid in distinguishing between causes and severity of liver injury and to help distinguish liver injury from damage to heart or muscles.
How is the sample collected for testing?
A blood sample is drawn from a vein in the arm.
NOTE: If undergoing medical tests makes you or someone you care for anxious, embarrassed, or even difficult to manage, you might consider reading one or more of the following articles: Coping with Test Pain, Discomfort, and Anxiety, Tips on Blood Testing, Tips to Help Children through Their Medical Tests, and Tips to Help the Elderly through Their Medical Tests.
Another article, Follow That Sample, provides a glimpse at the collection and processing of a blood sample and throat culture.
Is any test preparation needed to ensure the quality of the sample?
No test preparation is needed.