ALT, an enzyme appears in liver cells, with lesser amounts in the kidneys, heart, and skeletal muscles, and is a relatively specific indicator of acute liver cell damage. When such damage occurs, ALT is released from the liver cells into the bloodstream, often before jaundice appears, resulting in abnormally high serum levels that may not return to normal for days or weeks. The purpose of this blood serum test is to help detect and evaluate treatment of acute hepatic disease, especially hepatitis, and cirrhosis without jaundice. Also to assess hepatotoxicity of some drugs. The normal range for infants is twice that of adults.
Many medications produce hepatic injury by competitively interfering with cellular metabolism.
Tests commonly referred to as liver function tests or LFTs do not actually determine liver function. Instead, they are static, primarily diagnostic parameters that serve to detect liver disease rather than quantitate liver function. Rather than liver function tests, it is more useful to refer to these tests as serum liver tests and to mentally categorize them according to the pathophysiologic processes they truly reflect. Likewise, the serum bilirubin level reflects prehepatic, intrahepatic, and posthepatic factors, making the differential diagnosis of jaundice complex. Serum liver enzymes can create confusion for both patients and physicians for these tests are highly sensitive, but very nonspecific.