What Are ALT And AST In Blood Test?

Alanine transaminase (ALT), also called alanine aminotransferase (ALAT) and serum glutamate-pyruvate transaminase (SGPT), is a transaminase enzyme. Aspartate transaminase (AST) is an enzyme that is released when your liver or muscles are damaged. After blood tests, we normally get the results of the liver and kidney function test report. The parameters of ALT and AST are apparently listed in the reports. What are the ALT and AST? Here is a brief analysis of our two most common liver enzymes, alanine transaminase and aspartate transaminase.

Alanine Transaminase

Alanine transaminase is present in various cells, especially in hepatocytes. ALT is mainly in the cytoplasm of hepatocytes which is different with aspartate transaminase. ALT is an enzyme that catalyzes the process of converting glutamate to alanine by transamination. The transaminase content in liver is about 100 times that in blood, and the concentration of ALT in liver cells is 1000 to 5000 times higher than that in the serum. Once a small amount of ALT in a liver is released into the blood, the enzyme activity in the serum can increase significantly.

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When the permeability of the liver cell membrane changes, ALT overflows from the cell into the circulating blood. As long as 1% of the hepatocytes are necrotic, the enzyme activity in the blood can be increased by 100%. Therefore, transaminase, especially ALT, is a sensitive signal of acute hepatocyte damage. Comparing with aspartate transaminase, ALT is still more sensitive, more specific and more clinically useful.

In fact, many reasons can cause changes in the membrane permeability liver cells, such as fatigue, alcohol, colds and even emotional factors. The increase in transaminase caused by the above reasons generally does not exceed 60 units, and when the transaminase value is higher than 80 units, it has diagnostic significance.

It should be emphasized that as long as the liver has inflammation, necrosis, poisoning and other damage, ALT will be released from the liver cells into the blood, and the increase in ALT only indicates that the liver may be damaged.

The following conditions can cause ALT to rise:
1. Physiology: normal pregnancy, pregnancy poisoning, strenuous exercise, malnutrition, menstrual period and etc. These can cause ALT to rise;
2. Liver disease: liver disease, fatty liver caused by various bacteria, viruses, mycoplasma, chlamydia, fungi, parasites, cancer and etc.
3. Post-hepatic: disease in biliary tract, gallbladder and pancreas, biliary obstruction and etc.
4. Systemic: other organs also contain this enzyme such as heart, kidney, lung, brain, digestive tract, testis, muscle, platelets and etc.

The ALT level could be elevated when the following diseases happen including myocarditis, heart failure, pyelonephritis, lobar pneumonia, tuberculosis, influenza, measles, systemic lupus erythematosus, hyperthyroidism, diabetes, rheumatic fever, leukemia, parasitic diseases, leaflets, brucellosis, myocardial infarction and etc.

The normal range of ALT in most laboratory tests is 0-40 units. Most experts believe that if the ALT serum value exceeds 2.5 times of the upper limit (100 units) and lasts for more than half a month, hepatobiliary disease may be considered. If the measured value exceeds 20 times of the upper limit(800 units), it is confirmed to be caused by hepatobiliary diseases.

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Medical decisive level:
1. More than 300 units: a dangerous value for serious damage to liver cells.
2. 40 units or more: biological variations (such as obesity, drugs and etc.).
3. 20 units or less: biological variation and pathological changes can basically be excluded.

We often pay attention to the increase of liver enzymes in the clinic, but it is not good for the reduction of ALT activity. Some experiments have a minimum value of normal values, but we also should pay attention to the reduction of ALT activity. These are more common in pyridoxal phosphate deficiency, ultimate state of liver disease, renal dialysis, renal insufficiency and etc.

It should be noted that changes in ALT activity are not consistent with changes in liver pathology. Some patients with severe liver damage do not have ALT increases. Therefore, liver function damage needs to be judged in terms of other conditions.

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