ALT

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Alanine aminotransferase (ALT) is mainly found in various cells, especially hepatocytes. The content of aminotransferase in the whole liver is about 100 times that of blood. Normally, as long as a small amount is released into the blood, the enzyme activity in the serum can be significantly increased. In the acute phase of various viral hepatitis and drug-toxic hepatocyte necrosis, ALT is released into the blood in large quantities, so it is an important indicator for the diagnosis of viral hepatitis and toxic hepatitis. The concentration of alanine aminotransferase in liver cells is 1000 to 3000 times higher than that in serum. As long as 1% of liver cells die, the enzyme activity in the blood can be doubled. Therefore, transaminase (especially ALT) is a sensitive sign of acute liver cell damage.

Figure 1. Protein structure of ALT.

Clinical significance

ALT mainly exists in liver and heart tissue cells. When these tissues are affected, the enzyme activity increases. Generally, ALT exceeds the upper limit of the normal reference value by 2.5 times and continues to be abnormal for more than half a month as the standard for diagnosing hepatitis. Chronic HBV infections often have varying degrees of immune tolerance. Even if the ALT measurement result does not reach this value, if it persists for a long time, it can be diagnosed as hepatitis. This situation often indicates a more serious condition. Serum ALT determination has the characteristics of high sensitivity and poor specificity for the diagnosis of hepatitis. Many factors outside the liver can cause increased serum ALT activity, such as malnutrition, alcoholism, cardiomyopathy, cerebrovascular disease, skeletal muscle disease, infectious mononucleosis and pancreatitis. In addition, certain drugs and poisons that are toxic to the liver, such as chlorpromazine, isoniazid, quinine, salicylic acid preparations, ampicillin, carbon tetrachloride, organic phosphorus, etc., can also lead to increased serum ALT activity.

If the patient's alanine aminotransferase is too high, it should be taken seriously. Certain diseases may occur. Common diseases include the following:

First, viral hepatitis. For viral hepatitis, liver lesions are mainly caused by a variety of hepatitis viruses. During the onset of the patient, in addition to abnormal liver protein metabolism, the concentration of alanine aminotransferase will also increase significantly through serum examination.

• Second, liver cirrhosis. When a patient has elevated alanine aminotransferase, it may be cirrhosis of the liver. Liver cirrhosis is mainly caused by viral hepatitis that is not cured for a long time. After the onset, the patient will have complications such as hepatorenal syndrome if not treated. And hepatic encephalopathy.
• Third, liver cancer. After the patient develops liver cancer, the alanine transaminase in the body will not only increase, but the prothrombin and alkaline phosphatase will be higher than the normal range.
• Fourth, myocarditis. The so-called myocarditis mainly refers to the diffuse inflammation of the myocardium. Patients often have high alanine transaminase during the acute attack.

Elevated alanine transaminase may be caused by the above diseases. In order to better judge the disease, it is recommended that patients combine other examination items. If it is caused by viral hepatitis, it is best to take antiviral and liver protection. If the patient is caused by liver cancer, it is best to choose a treatment plan based on individual circumstances, such as surgery, chemotherapy, and radiotherapy.

Precautions

• When measuring serum alanine aminotransferase, the substrate and serum should be kept in a 37°C water bath beforehand, and then the substrate should be added to the serum for accurate timing.
• The serum sample should be separated from the blood clot quickly and measured in time. If it cannot be measured immediately, it should be placed in the refrigerator, but not more than 3 days. Hemolyzed specimens should not be measured, because the enzyme activity in the cells is high, which will affect the measurement results.
• During operation, the action time, temperature, pH value, reagent concentration and reagent addition amount should be accurately grasped, so as not to affect the measurement result.

References

1. Karmen A.; et al. Transaminase activity in human blood. The Journal of Clinical Investigation. 1955, 34 (1): 126–31.
2. Giannini EG.; et al.. Liver enzyme alteration: a guide for clinicians. Canadian Medical Association Journal. 2005, 172 (3): 367–79.