What Is an Alanine Aminotransferase?

Alanine aminotransferase (ALT) is an enzyme that is found mainly in the liver. It is also found in smaller quantities in other organs, such as the kidneys, heart, muscles, and pancreas. Formerly called serum glutamate pyruvic transaminase, ALT is now sometimes alternately known as alanine transaminase. ALT is commonly monitored by physicians in blood chemistry panels, and is particularly useful in liver function tests.

The alanine aminotransferase enzyme participates in the alanine cycle in cells. As an enzyme, it is a protein produced by the body to speed up a chemical reaction. ALT's specific function is to catalyze a reversible reaction that transfers an amino group from alanine to alpha-ketoglutarate, making pyruvate and glutamate. The activity of ALT is highest in hepatocytes, or liver cells, and striated skeletal and cardiac muscle cells. Through its role in the glucose-alanine cycle, ALT enables efficient muscle contraction by using muscle protein to produce glucose and disposing of wastes through the liver.

Both human and veterinary health professionals commonly measure ALT in blood chemistry panels. Elevated levels of ALT in the blood are a sign of hepatocellular injury, or liver cell injury. When liver cells are injured, ALT effectively “leaks” out of those cells, causing it to appear in higher concentrations in the blood panels. ALT is thus known as a leakage enzyme. It is often measured in conjunction with aspartate transaminase (AST), alkaline phosphatase, and bilirubin to evaluate liver disease.

Some common causes of elevated alanine aminotransferase include liver diseases such as cirrhosis, viral hepatitis, liver tumors, and ischemia, or lack of blood flow to the liver. Additional causes of elevated ALT include drugs that affect the liver such as statins, some antibiotics, chemotherapy, aspirin, narcotics, and barbituates.

ALT can also be elevated in other diseases such as pancreatitis, mononucleosis, or celiac disease. Sometimes, ALT levels are elevated due to recent cardiac catheterization or surgery. Individuals taking long-term medication, or those who have risk factors for liver disease are often monitored regularly for high levels of ALT.

A normal range of ALT resulting from an alanine aminotransferase test for an adult human is 0-40 units/liter. Ranges can vary, however, depending on genders, and even animal species. Test results may also vary from one testing laboratory to another.

Alanine aminotransferase test results can also be skewed by smoking cigarettes, medications, or pregnancy. Sometimes, performing strenuous exercise immediately before the test can skew results. Some herbs, such as echinacea or valerian, are also capable of increasing ALT levels in the blood.