In outpatient clinics, patients often come in with physical examination reports for abnormal liver function and elevated transaminases. What is the cause of elevated ALT? ALT is mainly found in liver cells and its intrahepatic enzyme activity is more than 1000 times higher than that in serum. Thus, a 1% inflammatory necrosis of hepatocytes can double the serum ALT activity. About 20 serum enzyme activities are changed in hepatitis, among which the change in ALT is the most sensitive, so it has been used for many years to diagnose liver diseases. Although elevated ALT is the main indicator of liver disease, there are many factors other than liver disease that can cause elevated ALT. So what are the causes of ALT elevation? We can divide them into two main categories: 1, due to liver disease itself, due to degeneration, inflammation and necrosis of liver cells, which increases the permeability of liver cells and causes ALT elevation due to enzymes being released into the blood, which can be seen in various types of viral hepatitis, cirrhosis, alcoholic liver, self-free liver, fatty liver, liver abscess, drug-related liver damage, etc. and liver damage caused by parasitic diseases. 2, factors other than the liver, the most common are: (1) biliary tract diseases that block the excretion of ALT and return to the blood, such as an acute attack of cholecystitis can cause a significant increase in ALT. (2) Tissue damage, such as severe burns and crush injuries; tissue necrosis, such as myocardial infarction, pulmonary infarction, pancreatitis; cancer systemic infection, etc. This is due to the presence of ALT in all organ tissues of the body except the liver. (3) A variety of pathophysiological conditions can also cause an increase in serum ALT, such as fever, staying up late, hunger, malnutrition, pregnancy, alcoholism, strenuous exercise, hypoxia, Chinese potatoes, toxin stimulation, as well as blood diseases, diabetes, tuberculosis, chronic nephritis, etc., can affect the vitality of ALT. Some causes can cause transient ALT elevation, such as fever, strenuous exercise, sleepless nights and hunger. Of course, the main cause of elevated serum ALT is viral hepatitis, which is caused by immunopathological damage to the liver that occurs between hepatitis virus infection and human immune function. In general, most of the acute hepatitis ALT returns to normal in 2-3 months, but if the course of the disease exceeds 6 months without recovery or if the ALT continues to rise repeatedly, it indicates that the hepatitis virus is constantly active and develops into chronic hepatitis. For hepatitis patients with persistent or repeatedly elevated ALT, the reasons are: (1) persistent infection with hepatitis virus and dysregulation of the body’s immune function cause chronic activity of the disease. (2) Patients with hepatitis have concomitant extrahepatic system diseases, such as combined myocarditis, hyperthyroidism, diabetes mellitus, ulcerative colitis, etc. It is difficult to reduce ALT to normal before the extrahepatic system diseases are recovered. (3) Fatty liver and alcoholic liver, due to too little activity or improper diet after the disease, excessive intake of sugar and fat, or continuous alcohol consumption, resulting in fatty infiltration of the liver, is a factor that cannot be ignored in causing persistent elevation of ALT. (4) Long-term, excessive drug consumption or improper application of some drugs can increase the burden on the liver and cause liver damage, which is also another cause of long-term ALT non-decreasing. For this reason, for every patient with elevated ALT, especially those with mild elevation, we should first look for and analyze what causes it, and also combine it with other laboratory tests and examinations to obtain an accurate diagnosis, and treat it differently and treat it symptomatically according to different situations.