Generality
Aspartate transaminase, more simply known as AST or SGOT (serum glutamic oxaloacetic transaminase), is an intracellular, cytoplasmic and mitochondrial enzyme, detectable in many tissues.
In particular, the dosage of aspartate transaminase in the blood is widely used to evaluate liver function .
What's this
AST is an enzyme belonging to the transaminase family, a group of proteins accumulated by the ability to catalyze the conversion of aspartate and alpha-ketoglutarate into oxalacetate and glutamate, and vice versa:
Oxalacetate + glutamate ↔ aspartate + α-ketoglutarate
What are transaminases?
Transaminases (or alanine amino transferases) are enzymes that take part in a series of biochemical reactions involving amino acids.
More in detail, transaminases regulate deamination, that is a reaction that transforms the amino acids in excess into ammonia. In fact, amino acids cannot be accumulated in the body, but must be transformed into energy: deamination is the first step in this process.
Usually, two specific types of transaminases are referred to:
- Aspartate aminotransferase (AST or GOT);
- Alanine amino transferase (ALT or GPT).
Both of these enzymes are present in the liver . However, small amounts can also be found in the blood stream and in various other tissues (heart, muscles and skeleton). These concentrations increase significantly in the presence of liver damage.
In the human body, aspartate transaminase exists in two different isoenzymatic forms, called GOT1 and GOT2 ; the first, cytoplasmic, abounds above all in the red blood cells and in the heart, while the second (GOT2), mitochondrial, prevails in the hepatic tissue.
Functionally, the cytoplasmic isoenzyme facilitates the formation of glutamate, while the mitochondrial enzyme facilitates the formation of α-ketoglutarate. Both isoforms require the presence of vitamin B6 to carry out their activity.
The chemical reactions mediated by aspartate transaminases are important in the process of interconversion of the amino acids, which in turn is important for adapting the protein synthesis to the needs of the body and filling any imbalances in their dietary reintroduction. Moreover, aspartate aminotransferase directs any amino acids towards energy use, while glutamate can be deaminated by oxidation with α-ketoglutarate resynthesis and release of ammonia (then converted into the non-toxic urea molecule).
Why do you measure
The AST-GOT determination is mainly required as a liver function test . Its serum content, in fact, increases in front of any cellular damage of the liver, up to the necrosis of the organ.
The specificity of this analysis is however low, in the sense that it gives us little information on the nature of the liver problem; moreover, being an enzyme present in various organs, there are many pathologies capable of inducing variations in the levels of aspartate transaminase in the blood.
For this reason, aspartate transaminase is often measured together with ALT: in case of cardiac or musculoskeletal damage, AST is higher than alanino amino transferase.
When is an AST examination required?
The doctor may prescribe the test to assess the levels of aspartate aminotransferase in different cases, both as a control and as a diagnostic tool for a specific pathological condition.
In most cases, this analysis is a good screening method to determine the presence of pathologies involving the liver.
The AST test is also useful if:
- Monitor the progress of a previously diagnosed liver disease;
- Check the effectiveness of any drug therapy.
Normal values
REFERENCE VALUES ASPARATO TRANSAMINASI (variable from laboratory to laboratory; a fast of 8-12 hours is required before collection)
MAN: up to 45 U / L
WOMAN: up to 30 U / L
AST Alta - Cause
An increase in aspartate aminotransferase can occur in cases of:
- Hepatitis;
- Cirrhosis and hepatic steatosis;
- Hepatic ischemia;
- Obstructive jaundice;
- Hypothyroidism;
- Tumor and liver metastasis;
- Severe burns;
- Muscle inflammation;
- Severe muscle trauma;
- Infectious mononucleosis;
- Kidney diseases;
- Obesity;
- Prostate cancer;
- Head trauma;
- Recent surgery;
- Myocardiopathies (myocardial infarction, pericarditis, etc.);
- Heart failure;
- Reye syndrome;
- cholestasis;
- Muscular dystrophy;
- Gangrene;
- Malignant hyperthermia;
- Metastasis to the bones;
- Hemopathies (haemolytic anemia, leukemia etc.);
- State of necrosis of the liver;
- Alcohol abuse;
- Pancreatitis;
- Eclampsia.
The causes behind a high level of AST can also be linked to other determinants, such as the use of certain drugs (including statins, ACE inhibitors, NSAIDs, heparin, labetalol, phenytoin, amiodarone and chlorpromazine).
AST Low - Causes
A reduction in aspartate aminotransferase may be due to:
- Vitamin B6 deficiency;
- Uremia;
- Habitual muscular exercise.
How to measure it
The examination is performed with a normal collection of peripheral blood from the vein of an arm.
What factors can influence the outcome of the exam?
Factors that can influence AST examination results include:
- Pregnancy can decrease AST levels;
- Many drugs can increase AST values due to their hepatotoxic action (among these we also have paracetamol);
- Alcohol abuse.
Preparation
Before undergoing a blood test for AST examination, it is necessary to observe a fast of at least 8-10 hours. During this period, it is possible to take only a small amount of water.
Also, before the exam, you must be in an upright position for at least 30 minutes.
Interpretation of Results
| ASPIRATORY HIGH TRANSAMINASE | AST - SGOT LOW | |
| Intrahepatic causes | Extrahepatic causes | Causes |
| Viral hepatitis | Myopathies (myositis, muscular dystrophies, delirium tremens, intramuscular hematomas, traumas, surgery, intramuscular injections) | Lack of vit. B6 |
| Hepatitis with or without jaundice | Habitual muscular exercise | |
| Poisoning by Amanita foulide | ||
| Acute alcoholic liver disease | Hemopathies (haemolytic anemia, leukemia) | |
| Drug hepatopathies | Myocardiopathies (myocardial infarction, pericarditis, etc.) | |
| Chronic hepatitis | Acute pancreatitis | |
| Cirrhosis | Renal infarction; pulmonary infarction | |
| Obstructive jaundice | Alcohol abuse | |
| Hepatic carcinomas, hepatic steatosis | Severe burns; recent surgery | |
NOTES: there may be moderate increases during treatment with various hepatotoxic or cholestatic drugs, such as anabolic steroids, cortisonics, barbiturates, anti-inflammatories, antibiotics, anesthetics, narcotics, statins.
Significant increases in AST occur in the presence of acute hepatitis, toxic liver necrosis or liver ischemia.
In chronic hepatitis, not in the active phase, in liver cirrhosis, obstructive jaundice and hepatic metastases increases are more contained.
Correlation with the results of other analyzes and interpretations
In addition to the AST, a very important transaminase is ALT (Alanine aminotransferase), a cytoplasmic enzyme which, similar to AST, is present in hepatocytes but also in non-hepatic tissues, where it is however in lower proportions than AST. It follows that in myocardial infarction the levels of AST increase significantly more than those of ALT (this condition is also accompanied by an increase in lactate dehydrogenase and creatine kinase).
The blood AST values peak about 24 hours after the heart attack, and then slowly return to normal within 3-7 days.
The AST / ALT ratio also increases in liver alcoholic diseases, cirrhosis and musculoskeletal injuries. In all other hepatocellular lesions, the increase in AST is instead generally lower than in ALT, and is also accompanied by an increase in lactate dehydrogenase and bilirubin.
