About ALT
ALT (Alanine Aminotransferase) is an enzyme found primarily in liver cells that leaks into the bloodstream when those cells are damaged, inflamed, or dying. It is the most liver-specific of the standard blood markers — a rising ALT is one of the earliest and most reliable signs of liver stress from fatty liver disease, alcohol, medications, or viral hepatitis. Many labs still use overly wide reference ranges; emerging research suggests ALT above 25 U/L in women and 35 U/L in men warrants investigation.