Serum ALT is the abbreviation of alanine aminotransferase, which used to be called alanine pyruvate transferase, abbreviated as GPT. This enzyme exists in liver cells, and when liver cells are damaged for various reasons, ALT penetrates from the liver cells into the plasma, and a significant increase in ALT can be detected by examination, which is often used in the diagnosis of various acute viral hepatitis in clinical practice. After infection with acute viral hepatitis, usually in 1-2 weeks, ALT will be significantly increased, and this is the most common test used to diagnose various viral hepatitis. In addition, for diseases such as alcoholic liver disease, drug-related hepatitis, fatty liver, and liver cancer, ALT will also appear to be significantly increased. Also, ALT can be mildly increased in cirrhotic patients with intra- and extra-hepatic bile duct stasis. Therefore, by testing ALT, we can make a clear judgment of the degree of liver damage.