Alanine aminotransferase, or ALT, is an enzyme found concentrated in the liver and in small amounts in the kidneys and the heart, states WebMD. An ALT test checks the blood for this enzyme, as its presence indicates potential liver damage. The enzyme's former name was serum glutamic pyruvic transaminase, or SGPT.
Although blood usually contains ALT in low levels, an unhealthy or impaired liver releases the enzyme in the bloodstream and raises the level of ALT in the blood, according to WebMD. In addition to checking for damage, doctors use the test to identify liver conditions such as cirrhosis, determine the cause of jaundice and keep track of medications that damage the liver. Normal values of ALT range between 10 and 40 units per liter for adult males and 7 and 35 units per liter for adult females.
The ALT test is one of many tests that check for liver damage collectively, adds WebMD. These tests include checking bilirubin levels; aspartate aminotransferase, or AST, levels; and lactate dehydrogenase, or LDH, levels. Tests for ALT and AST enzymes are the ones that give the most reliable results.
Raised ALT levels, while usually caused by liver problems, are also caused by medications, such as statins and antibiotics, and lead poisoning, according to WebMD.