ALT
What it measures, and what changes the number.
ALT (alanine aminotransferase) is an enzyme found mostly inside liver cells, with small amounts in muscle and other tissues. When liver cells are damaged, ALT leaks into the blood, so the test measures how much enzyme activity is present in serum or plasma.
It is typically ordered with AST, ALP, GGT, bilirubin and albumin as part of a liver panel. The pattern across these tests, and the relationship between ALT and AST in particular, gives more information than any single value.
Strenuous exercise in the days before a draw can raise muscle-related enzymes, and a hemolyzed sample can affect the reading. Some labs use methods that add a vitamin cofactor to the reaction and others do not, which can shift results between labs. Older reports call it GPT (glutamic pyruvic transaminase), and Spanish-language reports may print Alanina aminotransferasa (ALT/GPT) or Alanina-aminotransferasa (GPT).
Often read alongside: AST, GGT, ALP, Bilirubin (total), Albumin