There are at least 20 amino acids in the body that can undergo transamination reactions, and all of them require specific transaminases. Transaminases are essential “catalysts” (catalytic enzymes) in the metabolism of amino acids in the body. Transaminases are most active in skeletal muscle, liver, heart, brain, kidney, pancreas, spleen, etc. Testes, lungs, digestive tract, red blood cells, platelets, and serum also contain transaminases of different activities. Different tissues contain different amounts of various aminotransferases, such as alanine aminotransferase (ALT) according to its content: liver, kidney, heart muscle, brain; and aspartate aminotransferase (AST): heart muscle, brain, liver, kidney. When the tissue cells containing transaminases are destroyed or damaged, the corresponding transaminases can enter the blood stream, causing an increase in enzyme activity within the serum. The methods of checking transaminases include spectrophotometry, chromatography on paper and photoelectric colorimetry. Among them, the photoelectric colorimetric method is more commonly used, and its 1 unit is the viability of 1 microgram of pyruvate produced by 1 ml of serum after incubation at 26°C for 20 minutes. When the same patient is examined in different medical units, the results may not be consistent because of the different methods used. ALT and AST are the most important enzymatic indicators in liver function tests. most of ALT and AST are found in hepatocytes, with ALT mainly in the cell plasma and AST mainly in the mitochondria. When hepatocytes are damaged, ALT enters the blood first; when hepatocytes are severely damaged and mitochondria are endangered, AST also enters the blood. It can be seen that ALT is more sensitive to hepatocyte injury. However, hepatocytes are not the only place where ALT and AST are stored. Injuries to other organs such as kidney, heart muscle, pancreas, muscle, spleen, gallbladder and lung can also cause various degrees of elevated transaminases in the blood. ALT levels between 0 and 40 units are normal. If it is outside the normal range, it can be retested once to rule out the possibility of errors due to factors such as laboratory equipment failure and operating errors. If the ALT serum value exceeds 2.5 times the upper limit of normal and persists for more than half a month, hepatobiliary disease can be considered; if the measured value exceeds 20 times the upper limit of normal (the upper limit of normal ALT is 40 units, 2.5 times is 100 units, and 20 times is 800 units), it is generally said that it can only be caused by hepatobiliary disease and is mainly due to liver cell damage. As far as ALT is concerned, those with significantly higher levels are mostly liver disorders such as viral hepatitis, drug-related liver disease, alcoholic liver disease, autoimmune hepatitis and diffuse liver cancer. Of course, liver disease may also be insignificantly elevated, and those with elevated levels may decline as their condition improves. Even if viral hepatitis is confirmed, we cannot simply judge the disease by the degree of ALT elevation. For example, in heavy hepatitis, because there are fewer surviving liver cells, the amount of transaminases released into the blood is small. Acute rheumatic fever, myocardial infarction and other diseases can lead to moderate increases. Mild elevations can be seen in amebic liver abscess, advanced schistosomiasis and antimony treatment poisoning, acute pancreatitis, cholecystitis, rheumatic active heart disease, rheumatic myocarditis, toxic shock, influenza, prostate hypertrophy, nutritional liver disease, polycystic liver, tuberculosis, depressed liver, reticulocytosis, and cerebral hemorrhage. For a healthy person, an elevated or decreased transaminase level within the normal range does not mean that there is something wrong with the liver. Aminotransferases are very sensitive, and their levels fluctuate at different times of the day when they are checked. Strenuous exercise, overexertion or eating fatty foods may cause a temporary increase in aminotransferases. Transaminases can also be temporarily elevated during menstruation.